Product Overview

The FISHER 977HP is a self-operated differential pressure regulator built for the seal oil system of hydrogen-cooled generators. It compares the sum of hydrogen pressure and spring force with the seal oil pressure fed back through two external sensing lines, and repositions the valve plug so that the oil-to-hydrogen differential stays constant even as hydrogen pressure moves. The differential set point is adjustable by spring from 6 to 10 psig (0.4 to 1.4 bar). The valve uses a 2 in ANSI Class 150 steel flanged body rated for 150 psig (10 bar) maximum inlet and outlet pressure, and operates from -20 to 150 F (-29 to 60 C). Body steel, cage and plug aluminium, O-rings nitrile, diaphragm nitrile or nylon, stem and stem sleeve stainless steel. Oil sensing port 1/4 in NPT female, hydrogen sensing port 1/2 in NPT female.

Product Features

• Self-operated differential control, no instrument air, motor or external power required

• Adjustable 6-10 psig (0.4-1.4 bar) oil-to-hydrogen differential set point through the control spring

• 2 in ANSI 150 RF steel flanged body with 150 psig (10 bar) maximum inlet and outlet pressure

• Dual external sensing lines to the seal oil and hydrogen sides hold the differential steady as hydrogen pressure changes

• Nitrile or nylon diaphragm with stainless steel stem and sleeve, service range -20 to 150 F (-29 to 60 C)

Typical Applications

Hydrogen-cooled generator seal oil systems in power plants, seal oil skids and oil supply units, and like-for-like replacement of existing 977HP units during overhaul.

Selection Notes

Confirm flange size and rating, the required differential range and the sensing port threads before ordering. Spring and diaphragm kits are available separately. Send the unit tag number and we will check stock and lead time.