Types 7608–7668 and 7708–7768 direct acting relief valves



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STAINLESS STEEL
RELIEF VALVES

Type 14450

Types 14520 – 14580

Type 21500 direct acting

Type 14340 low pressure

14540, 14640 semi-capsule

7608–7768 direct acting

Direct acting relief valve.

Adjustable cracking pressure.

Reseals at 92% cracking pressure.

NACE Standard MR-01-75 compliant.

Designed as safety device rather than for pressure control.

Types 7608–7668 relief valves offer a choice of three orifice sizes, each with either 1/4" NPT female, or 1/2" NPT male, inlet connections. Types 7708–7768 offer the same configuration options, but with BSP rather than NPT connections. The valve is of the direct acting type, comprising a hexagonal section body in which a piston is spring loaded against a seat formed on the inner end of an inlet orifice. Spring loading, and hence valve cracking pressure, is adjustable by means of a screw at the upper end of the body.

The loading spring is immersed in the valve operating fluid, the spring chamber being connected to the valve outlet port through a fluid way in the piston. The possibility of fluid leakage via the threads of the spring adjusting screw is prevented by a sealing/locking cap fitted over the protruding end of the screw.

Special manufacturing materials ensure that the valve complies with NACE Standard MR-01-75 (latest revision as applicable) and is thus suitable for use in most fluid systems. It should be noted, however, that the valve is designed to function as a safety device and should not be used to control fluid pressure within a system.


Reseal pressure

92% cracking pressure or better.

  

Configuration options

    Pressure range Connection
Part No. Orifice (bar) (psi) inlet outlet
7608 5/32" 90 – 620 1,300 – 9,000 1/4"NPT F 1/4"NPT F
7618 1/8" 90 – 932 1,300 – 13,500 1/4"NPT F 1/4"NPT F
7628 5/32" 90 – 620 1,300 – 9,000 1/2"NPT M 1/4"NPT F
7638 1/8" 90 – 932 1,300 – 13,500 1/2"NPT M 1/4"NPT F
7648 3/16" 69 – 414 1,000 – 6,000 1/4"NPT F 1/4"NPT F
7668 3/16" 69 – 414 1,000 – 6,000 1/2"NPT M 1/4"NPT F
7708 5/32" 90 – 620 1,300 – 9,000 1/4"BSP F 1/4"BSP F
7718 1/8" 90 – 932 1,300 – 13,500 1/4"BSP F 1/4"BSP F
7728 5/32" 90 – 620 1,300 – 9,000 1/2"BSP M 1/4"BSP F
7738 1/8" 90 – 932 1,300 – 13,500 1/2"BSP M 1/4"BSP F
7748 3/16" 69 – 414 1,000 – 6,000 1/4"BSP F 1/4"BSP F
7768 3/16" 69 – 414 1,000 – 6,000 1/2"BSP M 1/4"BSP F

Operating media

Mineral oils, water-glycol mixtures with corrosion inhibitor.

Working temperature

Standard: –20°C to +150°C.
Arctic available on application.

Recommended filtration

10 micron.

Weight

1.25 Kg


Test procedure

Each valve is tested by Marshalsea Hydraulics and issued with a unique serial number prior to dispatch. The following describes the testing procedure.


  

1

Ensure compliance with internal procedure – safe system of work for manual test rigs.

2

Visually examine for external defects, damaged threads, etc.

3

Connect to the test rig as shown on the left.

4

Unscrew adjuster to minimum setting.

5

Raise pressure until valve functions – note performance of reseat. Repeat in increments of 2,000 PSI to the valve’s upper limit. Reseat must remain within 5% of cracking pressure at all times. Valves that fail to reseat within 5% are to be reworked.

6

Hold on pressure for approximately 2 minutes. Check for pressure decay and leakage.

7

Remove from test rig and immediately plug both ports.

8

Ensure that Test Certificate log is completed and mark valve with the information contained on the production documentation. Affix CE mark.

9

Pass to inspection.


© Marshalsea Hydraulics Limited – a member of the Bifold Fluidpower group of companies.

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