NPSHa - One large and one small pump on same suction manifold
NPSHa - One large and one small pump on same suction manifold
(OP)
Hi
I have come across a problem that and I don't quite know where to start.
The problem is as follows:
We have a 13 meter high tank, water level can be anywhere between 0 and 13 meters.
A small pump (3 m3/h, NPSHr = 3 meter) is placed 6.5 meters above the ground. The suction pipe is located on the suction pipe of a large pump (850 m3/h, it is all I know about this pump)1 meter in front of the pump inlet flange (yes, I know it is far from ideal). The large pump is being used to fill and empty the tank and located 2 meters above ground. The small pump is used to sample the water as the tank is being emptied, the large and the small pump is running at the same time.
Who do i solve the NPSHa for the small pump?
1. Normal NPSHa without taking into account the low pressure the large pump will create at its suction
2. Consider the suction piping for the large pump as a separate tank (for the small pump) with the pressure conditions we will see there and do NPSHa based on those values.
Or is there another way?
All help would be very much appreciated.
--Esporp
I have come across a problem that and I don't quite know where to start.
The problem is as follows:
We have a 13 meter high tank, water level can be anywhere between 0 and 13 meters.
A small pump (3 m3/h, NPSHr = 3 meter) is placed 6.5 meters above the ground. The suction pipe is located on the suction pipe of a large pump (850 m3/h, it is all I know about this pump)1 meter in front of the pump inlet flange (yes, I know it is far from ideal). The large pump is being used to fill and empty the tank and located 2 meters above ground. The small pump is used to sample the water as the tank is being emptied, the large and the small pump is running at the same time.
Who do i solve the NPSHa for the small pump?
1. Normal NPSHa without taking into account the low pressure the large pump will create at its suction
2. Consider the suction piping for the large pump as a separate tank (for the small pump) with the pressure conditions we will see there and do NPSHa based on those values.
Or is there another way?
All help would be very much appreciated.
--Esporp





RE: NPSHa - One large and one small pump on same suction manifold
Johnny Pellin
RE: NPSHa - One large and one small pump on same suction manifold
Without putting too much thought into it at this stage, your suggestion 2 sounds like the correct approach, establish the pressure at the pump inlet pipe at the interface with the main inlet line (worst case) and calculate from there.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
RE: NPSHa - One large and one small pump on same suction manifold
Sampling from the suction of the large pump was not optimal, but necessary due to adding of other chemicals downstream. The major problem was the original placement of the sample pump. On other installation this design has worked, however then with the sample pump installed lower than the large pump.
Thanks again!
--Esporp