I made a pressure valve

The intent is to be able to simulate an adjustable back-pressure.  When the pump operates, the water pushes against the spring.  When the pump stops, the spring pushes the plunger closed.  The more the tap is turned off, the higher the pressure.

1 Open the tap

Spring from Bunnings.

Measure the length.  Later I cut it back by a couple of mm

Cut the spring with a hacksaw

 

 

 

Reassemble the tap