PNID -Ideal Distance Between Pump & Valves

Ideal length PNID distance between Pump and valves

The problem of dis-alignment of pump from its present position is generally observed due to bad design in PNID which didn’t allow the medium to settle down and create unwanted pressure in the line and hence dis-alignment of pump and other accessories.

Given below is the typical pump station layout with valves at proper distance

Above given diagram is the ideal PNID describing the required distance valves should have from pump . Check valve should be at least 5 D distance from pump to absorb impact of surge and have enough time to close the valve plates with decreasing pressure of medium to prevent vacuum. 

Butterfly valve is used for opening and closing the valve and should be at least 3D distance from check valve. If check valve is less than 5D distance from pump than on closing of pump check valve will close and due to less distance to travel in pipe resultant qty of medium will be more and hence more pressure will create which moves back ward and form surge which will move in reverse direction and put pressure on pump due to which pump will get jerks due to back pressure and it will move from its present position. If there is distance of at least 5D between pump and check valve on closing the pump , due to large distance between pump and valve possibility of forming back pressure will get reduced and hence decrease in risk of back surge on pump.