The instructions that came with my accumulator:
At what pressure should I set the accumulator tank?
The pressure in the tank is adjusted by means of the air valve in the closed end.
The tank is supplied with an internal pressure of about 2.8 bar (35 psi). Reduce this pressure to
2 - 3 psi below the cut-in pressure of the pump (refer to pump instructions for details). This pressure adjustment is best done before installation of the tank, using a car-type pressure gauge to determine when the required pressure is reached, as follows:
i. Depress the central pin of the Schrader valve with your finger, to release gas
ii. Release gas a little at a time, until the pressure is correct
iii. If you release too much gas by mistake, air may be pumped back in with a hand - or foot-pump.
WARNING
Make sure that there is adequate ventilation when setting or adjusting pressure in an accumulator tank. Nitrogen is non-toxic, but oxygen levels may be reduced in confined spaces.
If the tank pressure requires adjustment after installation, ensure first that the pump is switched off and that an outlet is open, so that there is no pressure in the system. Then regulate the pressure as indicated above.
Check the accumulator tank performance in this way every 6 months, and adjust the pressure if necessary.
EXAMPLE
Pump Cut-in Acc. Tank Pressure Pressure setting
1 bar (15 psi) 0.8 bar (12 psi)
0.7 bar (10 psi) 0.5 bar (7 psi)
0.5 bar ( 7 psi) 0.3 bar (5 psi)