Metering pump is conveying small flow water pump
and flow requirements more precise, the flow of the metering pump is intermittent pulse flow, compared with the usually steady flow, pipe flow velocity in the change is big, friction loss and partial loss is cyclical change.
Similar is XuanBo flow leads to the velocity change, thus caused the loss to the acceleration produced, so when calculating the metering pump inlet NPSHa, besides considering the line loss, must also consider the influence of the loss of NPSHa acceleration.
A, how to calculate the metering pump NPSHa each related factors analysis, all the pressure for the absolute pressure: 1, the pressure source has two parts: 1)
Liquid surface pressure: can be atmospheric pressure, also can be artificially boost pressure;
Liquid level height difference of static pressure: above the center line of the pump head is positive, whereas negative.
2, frictional losses: 1)
The flow of materials through the system generated when frictional resistance;
Material through the pipe fittings and valves when the local resistance;
Produced by the material through the metering pump check valve resistance;
Material through the metering pump diaphragm support resistance 3, acceleration when the head loss: 1)
And material properties;
Related to piping system characteristics;
Saturation vapour pressure metering pump performance related material NPSHa computation formula is as follows: type: Pa: is the absolute pressure of the liquid surface, converted to liquid column height m;
Pz: static head (
Or static height, used to indicate a higher or lower than the import level;
Pf: it's under the big viscous friction loss import pipeline, valve and equipment;
Pvp: is liquid vapor pressure or pressure, gas liquefaction conversion into liquid column height m;
PACC: it is caused by the pressure loss of head acceleration.
How to calculate the acceleration of head loss: PACC: acceleration is head, m;
L: is the intake line length to m;
SG: is the proportion of liquid Q: single cylinder is single-acting pump flow, expressed in L/h;
N: is the plunger reciprocating frequency SPM per minute;
DP: is the inlet pipe diameter to mm said two, the definition of NPSH NPSH is English Net Positive Suction Head acronym.
The English translation is the meaning of & other;
Net positive suction head & throughout;
The pressure head is absolutely absolute pressure of vacuum as a benchmark.
Concept from the centrifugal pump NPSH, usually called NPSH again.
NPSH refers to the water pump suction unit weight of the liquid at the entrance of the surplus energy more than vaporization pressure, unit with & other;
M & throughout;
Metering pump NPSH and used by concept of NPSH of centrifugal pump is the same.
Three, the classification of NPSH NPSH into NPSHr (
Must be NPSH)
And NPSHa (
Effective NPSH, available NPSH, NPSH)
NPSHr is necessary in order to guarantee the normal work of the pump can be long-term stability guarantee allowance.
The parameters of the NPSHr is directly related to the pump itself, and the design of the pump, check valve structure, hydraulic structure and so on is directly related to import and export.
Is usually determined by plant experiment.
NPSHa is the device system can provide available for pump room.
NPSHa and system is the source of the pressure, the trend of the system pipe parameters and layout, material flow and flow velocity in the pipe line are directly related.
Has nothing to do with the structure of the pump.
Iv. The relationship between NPSHa and NPSHr for application in the concrete pump, we need the calculation for the actual system device: NPSHa (
Material saturated vapor pressure)
Pa / (
9 Kg/m3 density x.
NPSHr are provided by the pump manufacturer specific parameters to ensure the long-term stable operation of pump, the relationship between NPSHa and NPSHr must be: NPSHa> NPSHr
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