| Right listen carefully,I will say this only once,(mock german accent)
The relief valve opens at a pre-set pressure dictated by the spring fitted,it will only open when that pressure is reached,
The moment the pressure reduces the valve will close but the drop only needs to be slight.
The valve will open and close rapidly but the pressure will remain at the max level at all times whilst the engine is at high revs.
Some engines never reach relief pressure due to wear in crank etc
Hope that makes sense
Batesy | 
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