The issue of the acceleration head of metering pumps
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I would like to ask the experts: is the acceleration head of a metering pump provided by the equipment supplier or by the design institute? I took a look at the API675 specification; when calculating NPIPA, this acceleration head needs to be deducted. So does the manufacturer still need to subtract this acceleration head when calculating NPIPR? Is it not very meaningful to discuss NPSHA and NPSHR for metering pumps?
This certainly needs to be taken into account; otherwise, it’s easy to have insufficient inhalation. The longer and thinner the pipeline, the greater the impact. As for the calculations, simply provide the specific inlet conditions and the manufacturer can carry out the calculations for you; if the resulting value is insufficient, an inlet buffer can be added to compensate for most of the head loss due to inlet acceleration.
What information is needed to provide to the manufacturer in order to calculate the acceleration head? Is npipa equal to npsha minus the acceleration head? So is npipr equal to npshr minus the acceleration head? In that case, when calculating the net cavitation head as npipa minus npipr, isn’t the acceleration head being subtracted twice?
Generally, this velocity head loss is deducted when calculating NPSHa; it is not included in NPSHr. Acceleration head loss Hacc=0.016LQN/(D^2), where L is the length of the suction pipe in meters, Q is the pump flow rate in L/h, N is the number of reciprocations per minute of the pump in r/min, and D is the diameter of the suction pipe in mm
What does an accelerating pressure head refer to? I didn’t understand
An acceleration head is something that exists only in reciprocating pumps. It is related to factors such as the pump piston area, pumping frequency, rod length, and inlet pipe length. It is equivalent to having to take into account the sudden drop in pressure that occurs during suction by the reciprocating pump; such a drop can easily cause the medium to vaporize.