I have a problem with the priming of a small Tapflo PTFE double diaphragm pump.

It is sat approx half a metre above a drum of 15% Perocetic which it is meant to pump over into a larger container, sitting next to the tank of acid.

The hose is approx 15mm (ID) and the pump is running at around 3-4 bar. Once the pump is primed there is no issue, but because the pump probably only runs once a week when we do a CIP (clean in place) by the time we come to use it the suction tube has drained all its fluid back to the container and it wont pump (won't prime)

Is there any way I can keep the pump primed, or somehow make priming the pump easier?

You may want to try putting a chemically compatible soft seated foot valve at the inlet of the suction line.

Valuable advice from a professor many years ago:  First, design for graceful failure.  Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs.  Only then can practicality and economics be properly considered.

The foot valve will definitely solve your problem. It is not the drained suction line which causes the problem. The pump housings get drained, too. That is because the suction side balls and seats do not seal 100 % over a longer standstill period. So, check the valves (especially the seat as suggested by CH5OH). If they are not worn another combination of ball and seat (only suction side!) will help. You need a hard plastic (PTFE) seat without bevel. Take  ball on the seat out, put the ball onto the seat and check if there is a gap between ball and seat. That gap - if there is any - causes the problem.

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