(800) 378-1500
285 Portsmouth Ave. Stratham, NH 03885
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The Building Blocks for Water Treatment Equipment

“Everything but the Chemicals”

Northeast Pump and Instrument (NPI) specializes in the design, sale, installation and repair of chemical feed equipment, systems and instrumentation for water and wastewater treatment. Our involvement in the industry spans more than 30 years and our technical staff boasts over 100 years of combined industry experience.


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Pressure Relief Valves

back pressure valves

Griffco, diaphragm pressure relief valves are designed to protect chemical feed systems from over pressure damage caused by defective equipment or a blockage in the chemical feed line.

Robust construction ensures reliability in the rigorous service of municipal and industrial applications.

Available in sizes 1/4" through 2".

Materials of construction include PVC, CPVC, PP, PVDF, PTFE, 316 SS, Alloy 20, and Hastalloy C.



  • High Reliability / Low Cost
  • Robust, Machined Construction
  • Vulcanized PTFE/EPDM Diaphragm
  • Externally Adjustable 10 - 150 psi
  • Optional 20 - 350 psi
  • Ventable to Suction Line
  • Wide Range of Materials
  • Tamper Resistant Adjustment Screw


Griffco diaphragm pressure relief valves operate when the pressure in the chemical system exceeds the preset pressure of the valve. The diaphragm is held against the valve seat by an internal spring. When the preset pressure is exceeded the diaphragm is forced up and the chemical flow out of relief port, back to the chemical tank or to the suction side of the pump. The valves are preset for 50 psi, however they are field adjustable from 10 - 150 psi, (optional 350 psi) via the adjustment screw with the special tool. The relief valve should be set approximately 15 psi higher than the system pressure. Installation should be made as close to the pump as possible, without any valves or accessories between the relief valve and the pump.

(800) 378-1500
285 Portsmouth Ave.
Stratham, NH 03885