Pneumatics

Solenoid / Solenoid valves will have a coil each end ...Its possible... if you have this type.. for the valve to stay open till enough pressure is built up to operate the return of the internal spool....thus the ram stays open till minimum operating pressure is attained.
A solenoid / spring type doesnt suffer from this problem as the spring returns the internal spool.
Having said that solenoid / spring valves wont solve the actual problem you appear to have of low buffer tank pressure.

Woody

In that case theyre solenoid spring valves. As Ive put the 2.5kg buffer in (was 1kg) hopefully thtatll see an end to the problem.

Andy