I recently bought a small hand pump which I believe was originally designed as part of an engine starting system (diesel?). I intend to use it to pump stored rainwater around the garden but also to hydraulically test model boilers. However it has gross overcapacity for the latter task with a working pressure in excess of 3000psi and an output per cycle of 1.25 cubic inches.

If however, an adjustable relief valve in conjunction with a pressure gauge were to be incorporated into the pump output line it might be possible to use it to test small boilers without blowing them to kingdom come.

My question is, what type of relief valve do I require and where should it be located in the output line?

Thanks for your response Michael which I think sums things up in a nutshell.

I have already bought the pump but also in the past have made tender type pumps. The pump that I have bought is of similar design to a tender type pump and is of moderate dimensions….about 6inches long. As you have said, because it is capable of pumping to 3000psi…..a reflection on the quality of design I suspect……does not mean that it only pumps at 3000psi. Perhaps it would have been more understandable if I had said between 0psi and 3000psi. The output pressure is only proportional to the force applied to the piston through the pumping lever.

However because this pump's cylinder is of greater capacity than the average tender type pump it would not take much to exert more pressure than intended……..hence my requirement for an adjustable pressure relief valve to be used in conjunction with a suitable pressure gauge.

Thanks for those thoughts Michael. What you suggest I think would be quite feasible and worth serious consideration. I have also found some pressure relief valves used in domestic plumbing which are cheap and should maintain pressure in the region of 6 -10 Bar and these might be OK for my purposes. Alternatively I suppose I could just make a scaled up version of a steam safety valve.