MKS HPS 145 Vacuum Sentry Series User manual

Vacuum Sentry
TM
Safety V alve
HPSTM Products Series 145
Vacuum SentryTM
Safety Valve
Operation and Maintenance Manual
651 Lowell Street
Methuen, MA 01844
Main Telephone: [phone] p/n 100010033
www.mksinst.com Rev. A2

Vacuum Sentry
TM
Safety V alve
Part # 145 - _ _ _ _ _ - _ _ _ _ _ _ - _ _
Serial # _ _ _ _ _ _
Please fill these numbers and have
them readily available when calling for
service or additional information.
(The part number can be found on your
packing slip, and both the part number
and serial number are located on the
bottom side of the housing.)
For more information or literature, contact:
MKS Instruments, Inc.
Phone: [phone]
www.mksinst.com
2015 MKS Instruments, Inc., HPSTM Products Inc. All rights reserved
IgniTorr, LoPro, HPSTM and Cv are trademarks and MODUCELL, VACUUM SENTRYTM and AUTO-SOFT are registered
trademarks of HPSTM , a division of MKS Instruments, Inc. SensaVac and Baratron are registered trademarks of MKS
Instruments, Inc. Elgiloy is a registered trademark of Elgiloy Co. OFHCis a registered trademark of Amax, Inc. VCR is a
registered trademark of Cajon Company. Freon, Teflon and Krytox are registered trademarks of E.I. DuPont de nemours & Co.,
Inc. Dust-off is a trademark of Falcon Safety Products, Inc., Mountainside, NJ.

Vacuum Sentry
TM
Safety V alve
Table of contents
Table of contents ....................................................................... 3
Package Contents ..................................................................... 1
Symbols Used in this Manual .................................................... 1
General Description of Vacuum SentryTM ............................................................. 2
Operating PrinciplesVacuum SentryTM................................................................... 3
Vacuum SentryTM Operation Sequence .................................................. 4
Normal Operation - Open position................................................................................ 4
Power Interruption ......................................................................................................... 4
Valve closed - Mechanical pump vented ...................................................................... 5
Power restored .............................................................................................................. 5
Specifications ............................................................................ 6
Installation ................................................................................. 7
Electrical ................................................................................................. 7
Mechanical ............................................................................................. 7
Service ...................................................................................... 8
Disassembly ........................................................................................... 8
Repair of Subassemblies........................................................................ 9
Piston / Diaphragm Subassembly ................................................................................ 9
Nose Piece O-ring Replacement.................................................................................. 9
Bonnet Subassembly .................................................................................................. 10
Reassembly ................................................................................................................ 10
Troubleshooting ....................................................................... 12
Valve Cannot Be Pumped Down to High Vacuum ................................ 12
Valve Leaks in Closed Position............................................................. 13
Valve Closes Too Slowly ....................................................................... 13
Valve Opens Too Slowly or Not Completely ......................................... 13
Valve Fails to Open............................................................................... 13
Closing Causes Large Burst of Air into System ................................... 14
Solenoid Valve is Hot ............................................................................ 14
Factory Repair ...................................................................................... 15
Accessories / Part Replacement ............................................. 16
Product Warranty..................................................................... 17
Notes....................................................................................... 1

Package Contents
Vacuum Sentry
TM
safety V alve
1
Before unpacking your Series 145 Vacuum SentryTM, check all surfaces of
the packing material for shipping damage.
Please be sure that your Series 145 Vacuum SentryTM package contains
these items:
1 Series 145 Vacuum Sentry
TM
1 Series 145 Vacuum SentryTM Manual
Inspect the Series 145 for visible evidence of damage. If it has been damaged
in shipping, notify the carrier immediately. Keep all shipping materials and
packaging for claim verification. Do not return the product to HPS
TM
Symbols Used in this Manual
The first two symbols below, that may be located on your Series 145
Vacuum SentryTM , identify critical safety concerns. They are used
throughout this manual to further define the safety concerns associated
with the product.
The last two symbols identify other information in this manual that is
essential or useful in achieving optimal performance from the Series 145
Vacuum Sentry
TM
.
CAUTION: Risk of electrical shock.
CAUTION: Refer to manual. Failure to read message could result
in personal injury or serious damage to the equipment or both.
Failure to read message could result in damageto the equipment.
Calls attention to important procedures, practices, or conditions.

2
Vacuum Sentry
TM
safety V alve
General Description of
Vacuum SentryTM
HPSTM Products Series 145 Vacuum SentryTM is a safety valve, which
protects a vacuum system in the event of power failure by isolating the
vacuum system and venting the mechanical pump. This avoids oil back
up and allows the motor to restart the pump more easily. Vacuum
SentryTM is offered with the ISO-KF flange sizes and solenoid voltages /
frequencies most commonly found on mechanical pumps. Since it
operates with atmospheric pressure and activates upon loss of electrical
power, the novel design requires no external pressurized gas source.
Fast acting Vacuum SentryTM is light weight, constructed of vacuum
compatible materials, and maximizes pumping conductance. Lifetimes in
excess of 100,000 cycles are typical, which translates into years of
trouble free use in suitable environments. The opening burst is less than
the critical backing pressure for turbomolecular and diffusion pumps,
when appropriately sized mechanical pumps are used. The closing burst
minimized by the unique patented buffer volume design. Vacuum
SentryTM consumes little power. Installation is simplified, because the
standard ISO-KF dimensions are used for the NW 40 KF and NW 50 KF
sizes, allowing the valve to replace elbows, Tees, and crosses of the
same size. Even when the mechanical pump is equipped with an integral
anti-suckback valve, Vacuum SentryTM should be used, because the
pump’s integral valve will not vent it and is undependable.

Vacuum Sentry
TM
safety V alve
3
Operating Principles
Vacuum SentryTM
Vacuum SentryTM’s solenoid valve is connected in parallel with the
mechanical pump’s electrical supply either at its source or at the pump’s
switch. See figure 1. When the electrical power is on, the solenoid valve is
closed, allowing the pump to keep Vacuum SentryTM’s body and the vacuum
system evacuated. Interruption of electrical power to the mechanical pump
causes the solenoid valve to open admitting air into Vacuum Sentry
TM
causing it to close very quickly. This isolates the vacuum system from the
mechanical pump, while the pressure deferential between the outside
atmosphere and the vacuum system provides the force to maintain the
valve in its closed position without electrical or pneumatic power. With the
vacuum system isolated, a series of small orifices admits air to the inlet port
of the mechanical pump until it has risen to atmospheric pressure. When
the mechanical pump is restarted, it evacuates the area above the piston
until the pressure is lowered to approximately that of the vacuum system.
Vacuum SentryTM automatically opens again allowing the vacuum system to
be pumped at the full speed of the mechanical pump.

4
Vacuum Sentry
TM
safety V alve
Vacuum SentryTM Operation Sequence
The mechanical pump is connected to the port on the right
side and the vacuum system to the bottom port.
Normal Operation - Open position.
Power is on to mechanical pump and Vacuum SentryTM. The
mechanical pump, inlet side of the Vacuum SentryTM, and the
Vacuum SentryTM are all under vacuum at approximately the
same pressure. The spring is holding Vacuum SentryTM open,
and the vacuum system is exposed to the mechanical pump’s
full pumping speed.
Power Interruption
The Vacuum SentryTM solenoid loses its power, since it is
connected in parallel to that of the mechanical pump. The
solenoid opens to the atmosphere. Air enters the Vacuum
SentryTM through the solenoid and creates a higher pressure
above the piston than exists below it. The piston closes
rapidly (30 milliseconds). During this time only the inside of
the piston (buffer volume) is being filled, isolating the vacuum
system from any introduction of air. The figure shows the
piston in transit downward.

Vacuum Sentry
TM
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5
Valve closed - Mechanical pump vented
The piston is fully down and Vacuum SentryTM is fully
closed. The higher pressure above the piston forces it
against the valve seat, where the Viton O-ring makes a
vacuum tight seal. Air from the higher pressure area above
the piston continues through the small orifice in the top of
the piston into the inside of the piston, and through a second
small orifice in its side into the mechanical pump’s inlet port.
This vents the mechanical pump to atmospheric pressure
gradually. When the pump is fully vented, the pressure
above the piston, inside the piston, and in the mechanical
pump are the same (atmospheric). The pressure below the
piston, in the vacuum system, is still lower and the piston
remains down (closed), retaining the vacuum system under
vacuum.
Note that , given enough time, the pressure in the
vacuum system will rise due to outgassing, leaks, etc.,
or venting by the operator, and when the pressure is
high enough, the spring will open the piston and the
vacuum system will be at the same pressure as the
mechanical pump (atmospheric).
Power restored
The solenoid coil is energized causing the solenoid to
close, isolating the inside of Vacuum SentryTM from the
outside atmosphere. The mechanical pump evacuates the
inside of the piston through the small orifice in its side and
the area above the piston through the small orifice in the
top of the piston via the inside of the piston. When the
pressure above the piston is approximately equal to that in
the vacuum system, the spring pushes the piston upward,
fully opening Vacuum SentryTM. The vacuum system is now
back in normal operation and exposed to the full pumping
speed of the mechanical pump.

6
Vacuum Sentry
TM
safety V alve
Specifications
Nominal body ID 2 inches (50mm)
Leak rate
- body < 1 x 10-9 T-l/s
- seal < 1 x 10-9 T-l/s
Closing time 30 ms
Closing burst 1 x 10-3 T-l
Power 7 Watts @ 115 VAC
Materials
- body & flanges extruded aluminum A1 6061-T6
- piston machined aluminum A1 2024
- seals (O-ring & diaphragm) Viton
- guide pin 304 stainless steel
Temperature range (valve) 0o to 100o C
Temperature range (solenoid) 0o to 50o C
Venting time 10s/lof vented volume(NW 40 & 50)
50 s/l of vented volume (NW 25)