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Product Information

Type 8 Pressure Sustaining/Surplus Valve
Product Overview
 

The Type 8 pressure sustaining/surplus valves are designed to sustain and control the upstream pressure and pass surplus mediums into a zone where they can perform useful work or be
recovered and conserved. The type 8 has a larger piston area for the pressure to act upon, compared to a standard relief valve lid. This ensures a smoother operation, which is required due to the fact a sustaining valve is designed for constant use, unlike a relief valve. Valves are supplied in sizes quarter inch to six inch and can be manufactured in Gunmetal, Cast Steel and Stainless Steel with ends screwed female BSP or flanged ends to customers requirements. The standard set pressure range of the Type 8 is 0.70 to 9.00 Bar g, although higher and lower set pressures can be accommodated.
(Consult Broady Technical Sales Engineers for further information).

Specification

All valves are supplied with a nitrile diaphragm for air, gases, oils, etc. as standard, but other materials are available on request. Valves for steam service are supplied with a metallic diaphragm.

Description of Action
 

Pressure is admitted at the inlet and acts upon the large area of the piston, this is backed by a compression spring. To regulate the valve the spring is compressed an amount equal to the load acting against it, thus keeping the valve lid on its seat. As the pressure tends to increase above this setting, the extra load acting on the piston compresses the spring further and this allows the valve lid to leave its seat and excess pressure discharges to atmosphere or pump suction. Similarly when the pressure is decreased the spring overcomes the lighter load imposed on the piston and thus the
valve closes. Compressing the spring increases the set pressure, relaxing the spring decreases the set pressure.

Installation Instructions
 

Surplus valves are not usually fitted in the main pipeline as in the case of reducing valves. They should be fitted in a branch line from the main, in a horizontal position with the spring uppermost and the flow indicated by the arrow cast on the body. It is most important that the pipe is clean and free from dirt, scale etc.

Maintenance Information

Replacing an elastomer Diaphragm : When the valve is isolated from the pressure slacken off the spring. Remove the dome, spring, locknut, nut and piston. It will probably be found that the diaphragm will come away freely. After removal of the diaphragm the spigot on the body should be cleaned. Grind in the valve faces if necessary, and after replacing the valve see that the distance piece and the face of the body are level. Fit the new diaphragm, making sure that it is a good fit on the spindle. Care should be taken when tightening the fasteners in order to prevent damage to the diaphragm. Re-adjust the pressure as necessary by means of the adjusting screw.

Download the Datasheet here: Download the IOM here:
 

Type_8.pdf

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