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Surge Relief / Back Pressure Regulator Model 80 / 888 and 81 / 888

NOMINAL SIZE RANGE (mm) : 25, 100 TO 300 (80/888) or 40 TO 80 (81/888)
PN100 (80/888) or PN50 (81/888)
ANSI CLASS 600 (80/888) or ANSI CLASS 300 (81/888)


The model 80/888 or model 81/888 regulator is a pressure loaded valve consisting of a standard model 80 (or model 81) Ainsworth regulator connected to a nitrogen accumulator of suitable volume. A loading needle valve allows the regulator jacket and accumulator to be loaded to any desired pressure.
The model 80/888 or 81/888 regulator can be used either as a surge reliever (to protect pipework from pressure surges) or as a backpressure control in-line regulator. In backpressure control mode, the regulator is frequently used as second stage pressure reducer, for achieving high pressure reduction ratios (by providing backpressure to another first stage pressure reducing regulator).


  • The nitrogen accumulator is charged from an external source of nitrogen gas pressure, with the aid of aseparate loading hose assembly (gas loading line) which can be supplied on request. This allows the user to vary the loading pressure.
  • Model 80/888 or 81/888 regulator is supplied complete with accumulator, gas loading valve and pressure gauge.
  • There are no external moving parts which can be damaged, encrusted or corroded; thus reliable operation in harsh environments is assured. The only internal moving part is the flexible rubber tube.
  • The resilient seal of the rubber tube against the core assures tightness, even with impurities present in the medium. The regulator will always function in safety relief mode, even after a long period of inactivity.


The “set pressure” is defined as the inlet pressure at which flow starts. The “loading pressure” is the pressure to which the jacket and accumulator are loaded with the tube fully contracted on the core.
Before flow can even start, the inlet pressure must expand the tube against the loading pressure by forcing it away from the core until the ends of the outlet slots are just beginning to be uncovered. Before the regulator opens, the inlet pressure must rise to a value equal to the loading pressure, plus the tube expanding pressure, plus the rise in jacket pressure as the tube expands to opening position. This rise in pressure equals the sum of the following three components:
a. The loading pressure.
b. The tube expanding pressure.
c. The rise in jacket pressure (amount in excess of loading pressure) as the tube expands to position where flow just starts.
In order to produce a flow rate equal to the maximum rated capacity for the given conditions, the inlet pressure must increase 5% to 8% above the set pressure. This makes the inlet pressure under rated flow equal to the expanding pressure plus 110 to 115% of the loading pressure.
After the regulator has opened, it will shut off tightly again as soon as the inlet pressure drops to the closing pressure. This closing pressure will be somewhat less than the opening pressure.

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Contact Details:

Tel: (011) 433-3968
Fax: (011) 433-9107

Physical Address:

44 Harry Street
Johannesburg South