Cat pumps 7537 User manual

DATA SHEET

PRESSURE SENSITIVE REGULATING UNLOADER

FEATURES

• Maintains full system pressure while running in bypass without full

load on pump.

• Senses pressure built up from downstream flow changes and bypasses

flow to protect pump from overpressure.

• Minimum pressure fluctuations with alternating use of multiple guns.

• Multiple ports for convenient mounting.

• Color coded spring allows for easy identification and simple change

from one model to another.

• Standard unloaders are fitted with NBR O-rings. Optional O-rings are

available for higher-temperature and chemical compatibility.

• FPM – .0110 (7537. 0110)

• FPM – .0110 (7542.0110)

Brass Models: 7537, 7542

SPECIFICATIONS U.S. Metric

7537

Flow Range 1–21 gpm 3.8–80 lpm

Pressure Range 230–2600 psi 15.8–180 bar

7542

Flow Range 1–21 gpm 3.8–80 lpm

Pressure Range 800–4000 psi 55–275 bar

Model 7537 Shown

COMMON SPECIFICATIONS U.S. Metric

Maximum Operating Temperatures:

Standard NBR O-Rings 140° F 60° C

Stnd. NBR O-Rings (Intermittent) 195° F 90° C

Optional FPM O-Rings 240° F 116° C

Inlet Ports (2) ½" NPT(F) ½" NPT(F)

Discharge Port ½" NPT(F) ½" NPT(F)

Bypass Port ½" NPT(F) ½" NPT(F)

Weight 2.54 lbs 1.15 kg

Dimensions 7.57 x 3.96 x 1.74" 192.2 x 100.5 x 44.3 mm

Use only at above specifications to ensure proper unloader life and performance.

This Pressure-Sensitive Regulating Unloader can be converted

to a Secondary Relief Valve. See page 4 for Relief Valve conversion.

SELECTION

These pressure-sensitive regulating unloaders are designed for systems with

single or multiple pumps, solenoid (gate) valves, nozzles, standard or "weep"

guns.

Note: For multiple-pump systems, it is best to use a pressure regulator, not a

pressure-sensitive regulating unloader.

These pressure-sensitive regulating unloaders should meet both the desired

system flow (combined nozzle flow rate requirement) and the desired

system pressure.

Note: Operation below the minimum flow of the unloader causes the

unloader to cycle. Operation above the maximum flows of the

unloader causes premature unloader wear, cycling and prevents

attaining desired system pressure.

INSTALLATION

These unloaders operate properly when mounted in any direction, however,

it is preferred to keep the plumbing to a minimum and the hex adjusting

nut easily accessible. The best mounting location is directly on the pump

discharge manifold head.

There are two (2) inlet connections on these unloaders. Both are ½"

NPT(F) ports and are located on the short extension side and bottom.

An arrow and the word IN is cast into the body indicating the direction

of flow. Liquid from the manifold discharge goes through these

connections.

The discharge connection is a ½" NPT(F) hex fitting. An arrow and the

word OUT is cast into the body indicating the direction of flow. Discharge

plumbing for the spray guns, solenoid (gate) valves or nozzles are connected

to this port.

The bypass connection is a ½" NPT(F) port located on the side of the body.

The word BY-PASS is cast into the body. Bypass liquid is directed out of this

port and can be routed to a reservoir (preferred method), a drain or to the

pump inlet.

OPERATION

These pressure-sensitive regulating unloaders hold established system

pressure in the discharge line when the trigger gun is closed or solenoid

(gate) valve is closed or the nozzle is clogged, thus bypassing all unrequired

flow. Squeezing the trigger gun or opening the solenoid (gate) valve will

close the bypass and return to established system pressure.

PRESSURE ADJUSTMENT

1. Setting and adjusting the unloader pressure must be done with the

system “on.”

2. Start the system with unloader backed off to the lowest pressure setting

(counterclockwise direction).

3. Squeeze the trigger and read the pressure on the gauge at the pump.

Note: Do not read the pressure at the gun or nozzle.

4. If more pressure is desired, release the trigger, turn hex adjusting nut one

quarter turn in clockwise direction.

5. Squeeze the trigger and read the pressure.

6. Repeat this process until desired system pressure is attained.

7. Once the desired system pressure is reached, stop turning the hex

adjusting nut.

Note: Pressure is not set at the factory.

Notice: A minimum by pass flow of 5% of the unloader rated flow capacity

is required for proper unloader performance. If the entire flow is

directed through the nozzle (zero bypass) the “cushioning” feature

of the bypass liquid is eliminated and the unloader can prematurely

wear or malfunction.

8. If desired system pressure cannot be reached, review

TROUBLESHOOTING chart.

9. When servicing existing systems, follow adjustment procedures as stated

above.

Note: A secondary pressure safety relief device (i.e. pop-off valve, safety

valve) should be used along with this pressure-sensitive regulating

unloader. Final adjustment for the relief valve should relieve at

200 psi above the system operating pressure.

Note: By removing the check valve and spring, these unloaders can

function as a secondary relief valve.

Read all CAUTIONS and WARNINGS before commencing service or operation of any high-pressure system

TYPICAL UNLOADER INSTALLATION

1. Pressure Gauge

2. Relief Valve

Shown as a secondary Relief Valve

3. Pulsation Dampener

4. Pressure Sensitive Regulating Unloader

5. Triplex Plunger Pump

DISCHARGE

OPTIONAL

INLET

BYPASS

See page 4 for Relief Valve conversion.

SERVICING

Disassembly

1. Disconnect bypass, discharge and inlet plumbing from unloader.

2. Remove unloader from pump.

3. Secure body of unloader in a vise with hex adjusting nutsfacing up.

4. Remove discharge fitting and O-ring, spring and check valve with O-ring.

5. Examine check valve and discharge fitting for wear, spring for wear or

fatigue,and O-rings for cuts or wear. Replace as needed.

Note: While the discharge fitting is removed, inspect sealing area where

the check valve makes contact within the internal body of the unloader for

grooves, pitting and wear. If damage is found, stop the repair and replace

with complete new unloader. If not, proceed with disassembly.

6. Remove two (2) hex adjusting nuts by turning in a counterclockwise

direction.

7. Remove spring retainer and spring.

8. Examine spring and spring retainer for scale build up, fatigue or wear and

replace as needed.

9. Use wrench to unthread and remove piston retainer and piston stem

together from main unloader body.

10. Examine piston stem and piston retainer for scale build up, scoring,

pitting and wear and replace as needed. Examine O-rings and backup

rings for cuts or wear. Replace as needed.

11. Remove unloader body from vise and reposition in vise with bottom

inlet port facing up.

12. Remove inlet fitting with O-ring, seat spring and ball.

13. Remove unloader body from vise and reposition in vise with bottom

inlet port facing down.

14. Drive out seat and O-ring from the top side.

15. Examine seat, seat spring and ball for scale build up, scoring and wear

and replace as needed. Examine O-rings for cuts or wear. Replace

as needed.

Reassembly

1. Remove unloader body from vise and reposition in vise with bottom inlet

port facing up.

2. Lubricate and install O-ring onto outside diameter of seat.

3. Place seat with O-ring into unloader body with small inside diameter hole

facing up.

4. Place ball onto seat and then spring.

5. Lubricate and install O-ring onto inlet fitting. Thread in inlet fitting by

hand and tighten.

6. Remove unloader body from vise and reposition in vise with bottom inlet

fitting facing down.

7. Lubricate and install O-ring and then backup ring over threaded end of

piston stem small diameter groove.

8. Install backup ring, O-ring and then backup ring on opposite end of

threaded piston stem. Lubricate all parts.

9. Lubricate and install O-ring onto piston retainer.

10. Place threaded end of piston retainer over the threaded end of the

piston stem.

11. Place piston retainer and piston stem assembly into unloader body

with threaded end of piston stem facing up. Thread piston retainer into

unloader body by hand and tighten with wrench.

12. Apply Loctite® 242® to the bottom threads of the piston stem.

13. Hand thread one (1) hex nut onto piston stem and tighten with wrench.

14. Place spring over piston stem and then spring retainer onto spring with

stepped surface facing down.

15. Hand thread two (2) hex nuts onto piston stem.

16. Lubricate O-ring on check valve. Insert check valve with O-ring facing

into unloader body. Place spring onto check valve.

17. Lubricate O-ring on discharge fitting. Hand thread into unloader body

and tighten with wrench.

18. Remove unloader from vise.

19. Re-install unloader onto pump.

20. Reconnect bypass, discharge and inlet plumbing to unloader.

21. Proceed to PRESSURE ADJUSTMENT.

Loctite and 242 are registered trademarks of the Henkel Corporation.

Read all CAUTIONS and WARNINGS before commencing service or operation of any high-pressure system

TROUBLESHOOTING

Unloader cycles • Worn O-ring or check valve

• Fitting leaking downstream

• O-ring in gun worn

Liquid leaking

from bottom

• O-ring for seat or inlet fitting cut or worn

Liquid leaking

from middle

• O-ring for piston worn or cut

Unloader will not

come up to

pressure

• Not properly sized for system pressure

• Foreign material in unloader

• Piston O-rings worn

• Nozzle worn or too large

• Jam nuts not properly set

Extreme pressure

spikes

• Adjusting handle turned completely into unloader

• Restricted bypass or no bypass

• System flow exceeds unloader rating

PRESSURE READING

Approximate pressure

reading at gauge

Gauge between

pump/unloader

Gauge between

unloader/gun-nozzle-

valve

System in operation

(Gun open)

System pressure System pressure

System in bypass

(All guns, valves closed)

Low pressure

0–150 psi

System Pressure

+200 psi

ITEM PN MATL PN MATL DESCRIPTION QTY

7537 BB 7542 BB

402 31766 NY 31766 NY Handle, Adjustment 1

403 126521 STCP R 126521 STCP R Nut, Hex Adjusting (M8) 2

408 32090 STL — — Spring Pressure (White) 7537 1

— — 32092 STL Spring Pressure (Blue) 7542 1

409 —BB —BB Nut, Hex (M8) 1

410 32115 BB 32115 BB Retainer, Spring 1

412 76170 S76170 SStem, Piston 1

414 —PTFE —PTFE Backup Ring, Piston Stem 1

415 —NBR —NBR O-Ring, Piston Stem 1

425 76727 BB 76727 BB Retainer, Piston 1

428 —NBR —NBR O-Ring, Piston Retainer 1

429 —NBR —NBR O-Ring, Piston Stem 1

430 —PTFE —PTFE Backup Ring, Piston Stem 2

434 76022 S76022 SSpring, Seat 1

435 76706 SS 76706 SS Ball and Seat Assembly (2-Piece) 1

437 —NBR —NBR O-Ring, Seat 1

439 —NBR —NBR O-Ring, Inlet Fitting 1

440 —FBB —FBB Body 1

441 —NBR —NBR O-Ring, Check Valve 1

443 76745 BB 76745 BB Valve, Check with NBR O-Ring 1

76723 BB 76723 BB Valve, Check with FPM O-Ring 1

444 76722 S76722 SSpring, Check Valve 1

446 —NBR —NBR O-Ring, Discharge Fitting 1

455 76018 BB 76018 BB Fitting, Inlet [½" NPT(F)] 1

460 76024 BB 76024 BB Fitting, Discharge [½" NPT(F)] 1

462 30533 BB 30533 BB Plug, Inlet [½" NPT(M)] 1

468 76671 NBR 76671 NBR

Kit, O-Ring (Includes: 414, 415, 428,

429, 430, 437, 439, 441, 446)

After Week #41, 2016 (7537);

Week #29, 2016 (7542)

—76680 FPM 76680 FPM

Kit, O-Ring (Includes: 414, 415, 428,

429, 430, 437, 439, 441, 446)

After Week #41, 2016 (7537);

Week #29, 2016 (7542)

*See Tech Bulletin 120 for changes prior to Week #41/2016 and Week #29/2016.

EXPLODED VIEWPARTS LIST

Bold print part numbers are unique to a particular model.

Italics are optional items.

R Components comply with RoHS Directive. MATERIAL CODES (Not Part of Part

Number): BB=Brass FBB=Forged Brass FPM=Fluorocarbon

NBR=Medium Nitrile (Buna-N) PTFE=Pure Polytetrafluoroethylene S=304SS

SS=316SS STCP=Steel/Chrome Plated STL=Steel

To convert to optional handle assembly, remove items 403 (quantity 2), 410 and 409.

Then reassemble as shown in insert.

403

410

408

415

440

409

Bypass

Discharge

441

444

414

412

430

429

430

437

439

462

Inlet

434

455

Date Stamp Location*

Read as week/year

446

460

443

Inlet

402

Optional Adjustment Handle

435

428

425

PN 993368 Rev G 20371 3/21

Inlet

440

Bypass

Discharge

441

444

446

460

443

Inlet

Remove

REGULATING UNLOADER TO RELIEF VALVE CONVERSION

The 7537 and 7542 Pressure-Sensitive Regulating Unloaders are typically used as a primary

pressure regulating device. They can be converted to a Relief Valve to be used as a secondary

pressure relief device by removing the discharge check valve O-ring, and spring.

Unloader PN Modifications Converted Relief Valve PN

7537 Remove parts

441, 443, 444

7537.100 (NBR Seals) 7537.1110 (FPM Seals)

7542 7542.100 (NBR Seals) 7537.1110 (FPM Seals)

CAT PUMPS 1681 94th Lane N.E., Minneapolis, MN 55449-4324 P: (763)780-5440 F: (763)780-2958 E: techsupport@catpumps.com www.catpumps.com

• CAUTIONS AND WARNINGS

All high-pressure systems require a primary pressure regulating device (i.e. regulator, unloader) and a secondary pressure relief device (i.e. pop-off valve, relief valve). Failure to install such

relief devices could result in personal injury or damage to pump or property. Cat Pumps does not assume any liability or responsibility for the operation of a customer’s high-pressure system.

Read all CAUTIONS and WARNINGS before commencing service or operation of any high-pressure system. The CAUTIONS and WARNINGS are included in each Service Manual and with each

Accessory Data sheet. CAUTIONS and WARNINGS can also be viewed online at www.catpumps.com/dynamic-literature/cautions-and-warnings or can be requested directly from Cat Pumps.

WARRANTY

View the Limited Warranty on-line at www.catpumps.com/literature/cat-pumps-limited-warranty

©2021 Cat Pumps Inc. All rights reserved. All data contained in this document are based on the latest product information available at the time of publication. Cat Pumps reserves the right to make changes at any time without notice.

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