Gardner Denver VST55-90B Service manual

13-17-618
Version: 00
Dec 7, 2018
VARIABLE SPEED
TWO-STAGE
STATIONARY BASE-MOUNTED
COMPRESSOR
AirSmartCONTROLLER
MODELS
VST55-90B
55-75-90kW
60HZ
OPERATING AND
SERVICE MANUAL

13-17-618 Page 1
MAINTAIN COMPRESSOR RELIABILITY AND PERFORMANCE WITH
GENUINE GARDNER DENVER® COMPRESSOR PARTS AND SUPPORT SERVICES
Gardner Denver® Compressor genuine parts, manufactured to design tolerances, are developed for optimum
dependability –specifically for Gardner Denver compressor systems. Design and material innovations are the result
of years of experience with hundreds of different compressor applications. Reliability in materials and quality
assurance is incorporated in our genuine replacement parts.
Your authorized Gardner Denver Compressor distributor offers all the backup you’ll need. An AirSmart network of
authorized distributors provides the finest product support in the air compressor industry.
Your authorized distributor can support your Gardner Denver air compressor with these services:
1. Trained parts specialists to assist you in selecting the correct replacement parts.
2. Factory warranted new and remanufactured rotary screw airends. Most popular model remanufactured
airends are maintained in stock at the factory, for purchase on an exchange basis with liberal core credit
available for the replacement unit.
3. A full line of factory tested AEON™ compressor lubricants specifically formulated for use in Gardner Denver
compressors.
4. Repair and maintenance kits designed with the necessary parts to simplify servicing your compressor.
Authorized distributor service technicians are factory trained and skilled in compressor maintenance and repair. They
are ready to respond and assist you by providing fast, expert maintenance and repair services.
To Contact Gardner Denver or locate your local distributor:
visit: www.contactgd.com/compressors
or
call: [phone]
INSTRUCTIONS FOR ORDERING REPAIR PARTS
When ordering parts, specify Compressor MODEL, Method of Cooling, POWER and SERIAL NUMBER (see
nameplate on unit). The airend Serial Numbers are also stamped on top of the discharge bearing carrier castings.
All orders for Parts should be placed with the nearest authorized distributor.
Where NOT specified, quantity of parts required per compressor or unit is one (1); where more than one is required
per unit, quantity is indicated in parenthesis. SPECIFY EXACTLY THE NUMBER OF PARTS REQUIRED.
DO NOT ORDER BY SETS OR GROUPS.
To determine the Right-Hand and Left-Hand side of a compressor, stand at the motor end and look toward the
compressor. Right-Hand and Left- Hand are indicated in parenthesis following the part name, i.e. (RH) and (LH),
when appropriate.

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WARNING –PROHIBITION –MANDATORY LABEL INFORMATION
Gardner Denver Rotary Screw compressors are the result of advanced engineering and skilled
manufacturing. To be assured of receiving maximum service from this machine, the owner must exercise
care in its operation and maintenance. This book is written to give the operator and maintenance
department essential information for day-to-day operation, maintenance and adjustment. Careful
adherence to these instructions will result in economical operation and minimum downtime.
Boxed text formats are used, within this manual, to alert users of the following
conditions:
Safety Labels are used, within this manual and affixed to the appropriate areas of
the compressor package, to alert users of the following conditions:
Indicates a hazard with a high level of risk, which if not avoided, WILL result in
death or serious injury.
Equipment starts automatically
Cutting of Finger or Hand Hazard –Rotating
impeller blade
Cutting of Finger or Hand Hazard –Rotating fan
blade
Health Hazard –Explosive Release of Pressure
High Voltage –Hazard of Shock, Burn, or Death
Present until Electrical Power is Removed
Entanglement of Fingers or Hand/Rotating Shaft

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Indicates a hazard with a medium level of risk which, if not avoided, COULD
result in death or serious injury.
Asphyxiation Hazard –Poisonous Fumes or Toxic Gases in Compressed Air
Indicates a hazard with a low level of risk which, if not avoided, MAY result in a
minor or moderate injury.
Burn Hazard –Hot surface
PROHIBITION/MANDATORY ACTION REQUIREMENTS
Do not Operate Compressor with Guard Removed
Do Not Lift Equipment with Hook –No Lift Point
Handle Package at Forklift Points Only
Lockout Electrical Equipment in De-Energized
State
Loud Noise Hazard –Wear Ear Protection
Read the Operator’s Manual Before Proceeding
with Task

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SAFETY PRECAUTIONS
Safety is everybody’s business and is based on your use of good common sense. All situations or
circumstances cannot always be predicted and covered by established rules. Therefore, use your past
experience, watch out for safety hazards and be cautious. Some general safety precautions are given
below:
Failure to observe these notices could result in injury to or death of personnel.
Keep fingers and clothing away from rotating fan, drive coupling, etc.
Disconnect the compressor unit from its power source, lockout and tagout before working on the
unit –this machine is automatically controlled and may start at any time.
Do not loosen or remove the oil filler plug, drain plugs, covers, the thermostatic mixing valve or
break any connections, etc., in the compressor air or oil system until the unit is shut down and
the air pressure has been relieved.
Electrical shock can and may be fatal.
Perform all wiring in accordance with the National Electrical Code (NFPA-70) and any applicable
local electrical codes. Wiring and electrical service must be performed only by qualified
electricians.
Open main disconnect switch, lockout and tagout before working on the control, wait 10 minutes
and check for voltage.
Failure to observe these notices could result in damage to equipment.
Stop the unit if any repairs or adjustments on or around the compressor are required.
Do not use the air discharge from this unit for breathing –not suitable for human consumption.
An Excess Flow Valve should be on all compressed air supply hoses exceeding 1/2 inch
inside diameter (OSHA Regulation, Section 1926.302).
Do not exceed the rated maximum pressure values shown on the nameplate.
Do not operate unit if safety devices are not operating properly. Check periodically. Never
bypass safety devices.

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TABLE OF CONTENTS
Maintain Compressor Reliability And Performance With Genuine Gardner Denver Compressor Parts And
Support Services...........................................................................................................................................1
Instructions For Ordering Repair Parts .........................................................................................................1
Warning –Prohibition –Mandatory Label Information..............................................................................2, 3
Safety Precautions........................................................................................................................................4
Index..............................................................................................................................................................6
List Of Illustrations.........................................................................................................................................7
Section 1, General Information .....................................................................................................................8
Section 2, Installation..................................................................................................................................14
Section 3, Starting & Operating Procedures...............................................................................................21
Section 4, Controls & Instrumentation ........................................................................................................28
Section 5, Compressor Lubrication - Separation, Filtration And Controls ..................................................43
Section 6 - Heat Exchangers (Oil, Air), Axial Cooling Fans........................................................................52
Section 7, Air Filter......................................................................................................................................57
Section 8, Shaft Coupling............................................................................................................................59
Section 9, Minimum Pressure/Check Valve................................................................................................65
Section 10, Inlet Control Valve....................................................................................................................67
Section 11, Pressure Relief Valve ..............................................................................................................69
Section 12, Ventilation Fans, Filters (Electrical Enclosure) ........................................................................71
Section 13, Motor Lubrication .....................................................................................................................72
Section 14, Maintenance Schedule ............................................................................................................73
Section 15, Troubleshooting .......................................................................................................................75
This book covers the following models:
KW
PSIG
Air Cooled and
Water Cooled
Parts List
Controller
Manual
55, 75, 90
100 THRU 175
VST55-90B
13-17-503
13-17-600
NOTICE
Gardner Denver factory remanufactured replacement compressor
airend units are available from your authorized distributor, on an
exchange basis, for all rotary screw compressor units.

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INDEX
Air Filter............................................................55
Air Filter, Section 7...........................................55
Air Flow In The Compressor System.................8
Air-Cooled Units, Location ...............................15
Auxiliary Air Receiver.......................................17
Cold Weather Installation.................................17
Compression Principle.......................................8
Compressor Lubrication –Separation, Filtration
And Controls, Section 5................................41
Control Piping...................................................17
Controls & Instrumentation, Section 4 .............28
Cooling, Sealing And Lubrication.......................9
Discharge Service Line ....................................18
Electrical Wiring ...............................................18
Enclosure .........................................................16
Filter Inspection................................................69
Foundation .......................................................16
General Information, Section 1 ..........................8
Grounding.........................................................20
Heat Exchangers
Air-Cooled.....................................................51
Oil/Air............................................................50
Water-Cooled ...............................................52
Heat Exchangers (Oil, Air), Axial Cooling Fans,
Section 6.......................................................50
Inlet Control Valve............................................65
Inlet Control Valve, Section 10.........................65
Inlet Line...........................................................17
Installation For Cold Cold Weather Operation.17
Installation, Section 2.......................................14
Lifting Unit ........................................................14
Location............................................................14
Air-Cooled Units ...........................................15
Water-Cooled Units......................................15
Lubrication, Cooling And Sealing.......................9
Main Motor Grease Specifications...................70
Maintenance Schedule, Section 14 .................71
Minimum Pressure/Check Valve......................63
Minimum Pressure/Check Valve, Section 9.....63
Moisture Separator/Trap (Optional) .................17
Motor Lubrication .............................................70
Motor Lubrication .............................................20
Oil Filter............................................................45
Oil Reservoir Drain...........................................16
Oil System
Addition Of Oil Between Changes................44
Compressor..................................................41
Draining And Cleaning .................................44
Filling Oil Reservoir......................................45
Low Air Demand And Package Operation ...46
Moisture........................................................42
Oil Change Interval.......................................44
Oil Filter........................................................45
Oil Flow Control Valves................................46
Oil Mixing Valve............................................46
Oil Separation Reservoir/Coalescing Element
..................................................................47
Oil Sight Glass..............................................43
Oil Specifications..........................................41
Recommended Lubricant.............................41
Piping
Blow Down Valve .........................................18
Control..........................................................17
Water............................................................18
Pressure Differential Gauging..........................48
Pressure Relief Valve ......................................67
Prestart-Up Instructions...................................21
Quick Start Guide.............................................23
Safety Precautions.............................................4
Sealing, Lubrication And Cleaning.....................9
Service Check List...........................................71
Daily Checks ................................................71
Every 1000 Hours Operation........................71
Every 3000 Hours Operation........................71
Every 8000 Hours Operation........................71
Weekly Checks.............................................71
Yearly ...........................................................72
Shaft Coupling .................................................57
Shaft Coupling, Section 8 ................................57
Starting & Operating Procedures, Section 3....21
Starting The Unit..............................................25
Stopping The Unit............................................26
Troubleshooting, Section 15............................73
Ventilation Fans, Filters (Electrical Enclosure),
Section 12 ....................................................69
Ventilation Fans/Filters ....................................69
Warning –Prohibition –Mandatory Label
Information .....................................................2
Water-Cooled Units, Location..........................15

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LIST OF ILLUSTRATIONS
Figure 1-1 –Compression Cycle ..................................................................................................................8
Figure 1-2 –Package Illustration (Air-Cooled) –External Details ..............................................................10
Figure 1-3 –Package Illustration (Air-Cooled) –Internal Details................................................................11
Figure 1-4 –Package Illustration (Water-Cooled) –External Details.........................................................12
Figure 1-5 –Package Illustration (Water-Cooled) –Internal Details ..........................................................13
Figure 2-1 –Typical Compressor Room.....................................................................................................15
Figure 2-2 –Inlet Line Lengths ...................................................................................................................17
Figure 2-3 –Package Maximum Current Consumption Summary.............................................................19
Figure 2-4 –Line Reactor Sizing Recommendations .................................................................................20
Figure 4-1 –Electrical Enclosure Hardware ...............................................................................................29
Figure 4-2 –Piping And Instrumentation Illustration...................................................................................32
Figure 4-3 –Wiring Diagram –(Air-Cooled) Two-Stage VS Control .........................................................33
Figure 4-4 –Wiring Diagram –(Air-Cooled) Two-Stage VS Control .........................................................34
Figure 4-5 –Wiring Diagram –(Air-Cooled) Two-Stage VS Control .........................................................35
Figure 4-6 –Wiring Diagram –(Air-Cooled) Two-Stage VS Control .........................................................36
Figure 4-7 –Wiring Diagram –(Water-Cooled) Two-Stage VS Control....................................................38
Figure 4-8 –Wiring Diagram –(Water-Cooled) Two-Stage VS Control...................................................39
Figure 4-9 –Wiring Diagram –(Water-Cooled) Two-Stage VS Control...................................................40
Figure 4-10 –Wiring Diagram –(Water-Cooled) Two-Stage VS Control..................................................41
Figure 5-1 –Thermostatic Mixing Valve Element.......................................................................................48
Figure 5-2 –Pressure Dew Point Of Compressed Air................................................................................49
Figure 5-3 –Oil Coalescing Element ..........................................................................................................50
Figure 6-1 –Air Flow Chart.........................................................................................................................53
Figure 6-2 –Cooler Housing Side Covers ..................................................................................................54
Figure 6-3 –Water-Cooled Heat Exchanger Coolant Requirements .........................................................55
Figure 6-4 –Water Control Valve ...............................................................................................................56
Figure 7-1 –Air Filter (Standard) ................................................................................................................57
Figure 8-1 –Coupling Components............................................................................................................59
Figure 8-2 –Coupling Element ...................................................................................................................60
Figure 8-3 –Motor Removal Hardware.......................................................................................................61
Figure 8-4 –Coupling Installation Tool Kit..................................................................................................64
Figure 8-5 –Coupling Removal Tool Kit.....................................................................................................64
Figure 9-1 –Minimum Discharge Pressure/Check Valve...........................................................................66
Figure 10-1 –Inlet Control Valve (Body).....................................................................................................67
Figure 11-1 –Pressure Relief Valve...........................................................................................................69

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1-1
SECTION 1
GENERAL INFORMATION
Figure 1-1 –COMPRESSION CYCLE
COMPRESSOR –Your Gardner Denver Rotary Screw package is fitted with two (2) in-series single
stage, positive displacement rotary compressors using meshing helical rotors to effect compression.
Each pair of rotors is supported between high capacity anti-friction bearings located outside the
compression chamber. Single cylindrical roller bearings are used at each end of the rotors to carry the
radial loads. An additional angular contact ball bearing is located at the discharge end of each rotor to
carry axial thrust loads. The main rotor sits atop its gate companion, in an over-under configuration that
saves (compressor assembly) space and eases piping network.
COMPRESSION PRINCIPLE (Figure 1-1) - Compression is accomplished by the main and gate rotors
synchronously meshing in a one-piece cylinder. The 1st stage main rotor has three (3) helical lobes, 120
apart, which mesh with five (5) helical grooves, 72apart, on its matching gate rotor. The 2nd stage main
rotor has four (4) helical lobes, 90apart, which mesh with five (5) helical grooves, 72apart, on its gate
rotor.
The air inlet port is located on one side in of the compressor cylinder near the drive shaft end. The
discharge port is in the diametrically opposite end of the compressor cylinder. Figure 1-1, rotates
compressor on its side to show inlet and discharge ports. The compression cycle begins as the rotors
unmesh at the inlet port and air is drawn into the cavity between the main rotor lobes and gate rotor
grooves (A). When the rotors pass the inlet port cutoff, air is trapped in the interlobe cavity and flows
axially with the meshing rotors (B). As meshing continues, more of the main rotor lobe enters the gate
rotor groove, normal volume is reduced and pressure increases.
Oil is injected into the cylinder to remove the heat of compression and seal internal clearances. Volume
reduction and pressure continues to increase until the air/oil mixture trapped in the interlobe cavity by the
rotors passes the discharge port (C). Each rotor cavity follows the same “fill-compress-discharge” cycle in
rapid succession to produce a discharge air flow that is continuous, smooth and shock free.
AIR FLOW IN THE COMPRESSOR SYSTEM (Figure 4-2, page 32) - Air enters the air filter and passes
through the inlet butterfly valve to the 1st stage compressor. After compression, the air/oil mixture passes
into the inter-stage manifold, where further oil injection may take place to maintain optimal system
temperature, and is subsequently delivered to the 2nd stage compressor. After 2nd stage compression,
the air/oil mixture enters the oil reservoir where most of the entrained oil is removed by centrifugal action
and drained down into the reservoir. The air and remaining aerosols pass into a coalescing element
where the oil is captured and drained through a drain line back into a lower pressure region - the inter-
stage manifold. The nearly oil-free air passes through the minimum pressure valve, aftercooler, optional
moisture separator, and finally to the distribution network.

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1-2
LUBRICATION, COOLING AND SEALING (Figure 4-2, page 32) - Oil is forced by differential pressure
from the oil reservoir through the oil cooler, thermostatic mixing valve, oil filter, distribution manifold, and
enters the compressors and inter-stage manifold. A portion of the oil is directed to internal passages, on
both 1st and 2nd stage airends, to lubricate the bearings and shaft oil seals. The balance of the oil is
metered by solenoid valves and orifices and injected into the 1st stage compressor rotors and inter-stage
manifold to remove the heat of compression, seal internal clearances and lubricate the rotors.

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1-3
Figure 1-2 –PACKAGE ILLUSTRATION (AIR-COOLED) –External Details
300ETK804-D
(Ref. Drawing)
Page 1 of 2

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1-4
Figure 1-3 –PACKAGE ILLUSTRATION (AIR-COOLED) –Internal Details
300ETK804-D
(Ref. Drawing)
Page 2 of 2

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1-5
Figure 1-4 –PACKAGE ILLUSTRATION (WATER-COOLED) –External Details
301ETK804-D
(Ref. Drawing)
Page 1 of 2

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1-6
Figure 1-5 –PACKAGE ILLUSTRATION (WATER-COOLED) –Internal Details
301ETK804-D
(Ref. Drawing)
Page 2 of 2

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2-1
SECTION 2
INSTALLATION
GENERAL - On receipt of the unit, check for any damage that may have been incurred during transit.
Report any damage or missing parts as soon as possible.
Do not electric weld on the compressor or base; bearings can be damaged by
passage of current.
LIFTING UNIT - Proper lifting and/or transporting methods must be used to prevent damage. Lifting slots
are provided in the base for tow motor use. The unit may also be moved into location by rolling on bars.
Lift compressor package by base only. Do not use other places such as
motors, compressors or discharge manifold piping as lifting points.
The eyebolts or lugs provided on the motors are for lifting the motors only and
should not be used to lift any additional weight. All eyebolts must be securely
tightened. When lifting the motors, the lifting angle must not exceed 15
degrees. Failure to observe this warning may result in damage to equipment or
personal injury.
Compressor, air/oil reservoir, separator chamber and all piping and tubing may
be at high temperature during and after operation.
LOCATION - The compressor package shall be installed, whenever possible, in a clean, well-lighted,
well-ventilated area with ample space all around for maintenance. Select a location that provides a cool,
clean, dry source of air. In some cases it may be necessary to install duct work to reach

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2-2
a source of adequate cooling air, or to direct cooling air in and out of the compressor package to prevent
re-circulation (e.g., not cooling the air entering the fresh air inlet). The package is designed to operate at
ambient temperatures ranging from 40F to 113F (at up to 1000 meter elevation). Contact your local
distributor for package operation at conditions exceeding the stipulated values.
A typical ventilation arrangement is shown in Figure 2-1.
Figure 2-1 –TYPICAL COMPRESSOR ROOM
When selecting the compressor package location, be aware that its noise level may increase above its
advertised free-field condition by reflections from nearby objects (e.g., walls, machinery, etc.) or by noise
from nearby machinery.
Air-Cooled Units - A combination oil/air cooler is supplied as standard equipment on all air-cooled
packages. The heat exchangers require sufficient cooling air flow to operate efficiently –please refer to
Section 6, Fig 6-1, page 53 of this manual for detailed instructions on the operation and maintenance of
air-cooled heat exchangers, including minimum heat exchanger cooling and enclosure ventilation
requirements.
Air for heat exchanger cooling is drawn in at the cooler end of the enclosure and is exhausted through a
roof vent. Air for motor cooling and for the compressor intake is drawn in at the controller end and
exhausted at a smaller roof vent. Refer to Package Illustrations on Figure 1-2 and Figure 1-3, pages 10
and 11, for hardware details.
Do not block flow of air entering or exiting the enclosure - allow 3-1/2 feet (1.1 m) clearance to the nearest
obstruction all around and on top.
Water-Cooled Units –Separate shell-and-tube coolers for air and oil services are supplied on water-
cooled packages. The heat exchangers require sufficient cooling water flow to operate efficiently –please
refer to Section 6 of this manual for detailed instructions on the operation and maintenance of water-
cooled heat exchangers, including minimum cooling water flow requirements.

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2-3
Air for motor cooling and for the compressor intake is drawn in at the controller end and exhausted at a
smaller roof vent –refer to Section 6 of this manual for enclosure ventilation requirements. Refer to
Package Illustrations on Figure 1-4 and Figure 1-5, pages 12 and 13, for hardware details.
Do not block flow of air entering or exiting the enclosure - allow 3-1/2 feet (1.1 m) clearance to the nearest
obstruction all around and on top.
FOUNDATION - The Gardner Denver Rotary Screw compressor requires no special foundation, but
should be mounted on a smooth, solid surface and as near level as possible. Temporary installation may
be made at a maximum 10angle lengthwise or 10sidewise.
Mounting bolts are not normally required. However, installation conditions such as piping rigidity, angle of
tilt, or danger of shifting from outside vibration or moving vehicles may require the use of mounting bolts
and shims to provide uniform support for the base.
OIL RESERVOIR DRAIN - The oil drain is piped from the bottom of the reservoir to the side of the base.
This drain is approximately 4.50 inches (115 mm) above the floor level. If this is not sufficient to
conveniently drain the oil, other methods are:
1. Elevate the compressor unit on a suitable structure to obtain the desired drain height.
If the compressor unit base is raised above floor level, the space between the
floor and the base bottom must be closed with solid material all around to
prevent main motor from running hot.
2. Construct an oil sump or trough below the floor level and pump or bail the drained oil.
3. Pump oil from the reservoir filler opening or drain to a container.
ENCLOSURE - The compressors, electric motors and oil/air cooler assembly are mounted inside the
enclosure. Service doors are provided for maintenance access. Be sure to allow enough space around
the unit for the doors to open completely.
To remove the enclosure doors, open the door and lift it up slightly to disengage the hinges.
Ducting may be required on air-cooled enclosed machines.

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2-4
INSTALLATION FOR COLD WEATHER OPERATION - It is recommended that the unit be installed
inside a shelter that will be heated to temperatures above freezing (40F, 5C). This will eliminate many
of the problems associated with operating units in cold climates where freezing rain, drifting snow,
freezing condensate and bitter cold temperatures are encountered.
Unsheltered (outside) installations should be avoided whenever possible. Installation next to a heated
building where enough heat can be used to keep the compressor room above freezing will save many
complications in the operation and installation of the unit.
Refer to Engineering Data Sheet 13-9-411, available from an authorized Gardner Denver distributor, for
the advantages of using the heat recovered from rotary compressors. This heat recovery could easily
pay for an adequate shelter for the unit.
AUXILIARY AIR RECEIVER - An auxiliary air receiver is not required if the piping system is large and
provides sufficient storage capacity to prevent rapid cycling. An adequate receiver capacity for the VST
units is 1/2 gallon for each cfm delivered by the compressor package.
OPTIONAL MOISTURE SEPARATOR/TRAP –The unit can be provided with an optional stand-alone
combination moisture separator and trap that is field-installed downstream of the aftercooler.
CONTROL PIPING - Control piping is not necessary since the Gardner Denver compressor package is
factory wired and piped for the control system specified.
INLET LINE - Where an inlet line is used between the air filter and the compressor, it must be thoroughly
cleaned on the inside to prevent dirt or scale from entering the compressor. If welded construction is
used, the line must be shot blasted and cleaned to remove welding scale. In either case, the inlet line
must be coated internally by galvanizing or painting with a moisture and oil-proof sealing lacquer. Up to
ten (10) feet (3 meters) in length, the inlet line should be the full size of the inlet opening on the
compressor. If an extra-long line is necessary, the pipe size should be increased according to Inlet Line
Length Chart Figure 2-2
Accessibility for inlet air filter servicing must be considered when relocating the filters from the unit to a
remote location.
Length of Inlet Line
Diameter of Pipe Size
0 to 10 Feet (0 to 3 Meters)
Same as Compressor Inlet Opening
10 to 17 Feet (3 to 5 Meters)
One Size Larger Than Inlet Opening
17 to 38 Feet (5 to 11.5 Meters)
Two Sizes Larger Than Inlet Opening
Figure 2-2 –INLET LINE LENGTHS
Do not operate the compressors with the fan or coupling guard removed.
Exposed fan and couplings may cause personal injury.

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2-5
DISCHARGE SERVICE LINE - The discharge service line connection on both water-cooled and air-
cooled units is located at the center roof area of the enclosure. Gardner Denver compressor packages
are inherently isolated from the service line by their own minimum pressure/check valves. Installer or end
user must ensure that other compressors that are piped into a common pipe manifold with the Gardner
Denver compressor package are each provided with an isolation check valve. It is recommended that an
additional receiver be installed between the rotary screw and reciprocating compressors sharing a
common pipeline. Do not install another check valve in the unit’s discharge line as operational upsets will
occur.
Discharge air used for breathing will cause severe injury or death.
Consult filtration specialists for additional filtration and treatment equipment to
meet health and safety standards.
BLOW DOWN VALVE PIPING –The blow down valve is vented between the air filter and inlet valve,
thus avoiding the need of any external pipe work.
WATER PIPING (Water-Cooled Heat Exchanger Models Only) - On machines equipped with water-
cooled heat exchangers, the water inlet and outlet connections are located in the unit base flange.
It is mandatory that any water-cooled unit be installed in a shelter heated to
temperatures above freezing (40F., 5C).
Please refer to Section 6, page 49 of this manual for detailed instructions on the installation, operation
and maintenance of the water-cooled heat exchangers.
ELECTRICAL WIRING - The compressor package is (internally) factory wired for use with the voltage
specified on the order - it is only necessary to connect power supply and ground wires to the provided
wire blocks.
Electrical shock can cause injury or death. Open main disconnect switch,
lockout and tagout before working on control box.

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2-6
Gardner Denver Guidelines for proper wiring, grounding and feed power conditioning - This
compressor package is provided with variable speed drives (VFD’s) to control compressors and cooling
fan motors. The indicated Gardner Denver guidelines for proper wiring, grounding, and feed power
conditioning must be followed in order to protect the VFD electronics. Failure to do so will void your
warranty.
Electrical Wire Sizing –A certified electrician familiar with National Electric Codes and applicable local
codes shall size the electrical power wires serving the compressor package. Refer to Figure 2-3, for a
summary of maximum package current consumption values.
460 VOLT VST55A, VST75A and VST90A MINIMUM COPPER SUPPLY WIRE RECOMMENDATIONS
460 V
VST-55 through VST 90
Minimum Copper Supply Wire
Recommendations
Model
Minimum Supply
Conductor
Ampacity
Minimum 75°C
Copper Wire
Sized @ 30°C
Minimum 75°C
Copper Wire
Sized @ 40°C
Minimum 75°C
Copper Wire
Sized @ 45°C
Notes
VST 55
162
2/0
3/0
3/0
VST 75
182
3/0
4/0
4/0
VST 90
220
4/0
250
300 or 2/0 (2)
{1}
Notes: Wire sizes are per Table 310.15(B)(16) in the National Electrical Code (NEC)
[1] 2/0 and 3/0 wires sized with derate for two parallel sets of conductors in a single conduit.
[2] Wires sized with derate for two parallel sets of conductors in a single conduit.
[3] Wires sized for 2 parallel sets of conductors in 2 conduits (1 set in each conduit).
Figure 2-3 –PACKAGE MAXIMUM CURRENT CONSUMPTION SUMMARY
The appropriate installation and use of 75ºC wire is the responsibility of the electrical professional(s)
performing the installation and must be per NEC, local and state regulations as allowed. All of the above
recommended minimum wire sizes are based on all terminal connections being rated at 75ºC minimum
temperature rating and copper wire run lengths of 100 feet or less. Please note that all UL-508A listed
control panels are rated for 40ºC ambient conditions.