Hi All

I've been trying to construct a pressure regulating device, using a 12v
latching solenoid and conventional valve, to protect a filter in a home
irrigation system. I am using a pressure switch which goes contacts
open at high pressure/contacts close at falling pressure. These two
states in turn trigger 555 timers which in turn drive small 12v SPDT
relays.

The relays are configured so that in the relaxed state the circuit
connects to the 0v line and when exited by the pulse from the 555,
switches to supply 12v for each relay in turn. The purpose of this
switching configuration is so that the 12v latching solenoid, which
operates the valve, can be switched to close the valve when pressure
reaches a high threshold, but then by reversing the supply voltage, is
switched to open the valve at a low threshold.

This all works perfectly - until the latching solenoid is connected,
whereupon the action of the solenoid causes the relays to bounce
erratically.

I have tried various combinations of (non polarised) capacitors and R/C
combinations across the terminals of the solenoid, and/or across the
relay. I have also tried using seperate 12v power supplies to power
the two sides of the device (timing - relay activation side and power
supply for solenoid side)but the action of the solenoid still causes
the relays to bounce erretically.

I feel I am running out of options to solve this dilema, but am now
considering the use of switching transistors or solid state relays.
Only I'm not sure how to switch such devices on and off to give the
necessary pulse to switch the solenoid on then off etc.

Any help would be greatly appreciated