Pump discharge calculation without flowchart how we can calculate flowrate by using pressure differenc?

Question

actually i need a simple equation to calculate pump discharge by using differential pressure (P1 & P2). can u drive and give the equation

Answer 1

The simplest way is using the definition of power for hydraulics:

Power * ε = Pressure * Flowrate

Easiest way to get power is to use a clamp-on ammeter on the motor, and multiply times voltage to get power. Typical larger motor is about 90% efficient, about 80% for small motors. An assumed efficiency of 80% for a 5 HP or better pump inside its operating range is generally reasonable. Somewhat lower for small pumps, say 60%. Multiply the two together for the ε in the equation above.

Pressure would be the pressure difference.

Make sure units are comparable:

1 HP = 746 Watts/sec = 550 ft-lb/sec

Pressure in lb/in^2 for US, kPa or MPa for SI.

Q (flowrate) in ft^3/sec for US, m^3/sec for SI.

This is a rough estimate,  accuracy is probably in the ±20% range.  To get better than this, you will have to take more complex measurements. Having pump curves is also useful. Most manufacturers have theirs posted on their websites now. For critial applications, you can generally get flowmeters with bettter than 0.5% accuracy.

Answer 2

The basic pump power equation is

BHP = GPM (THD) SG / 3.96 (%Eff)

If the fluid is cold water the pressure conversion is 1 psi = 2.31 Ft of TDH. The SG for water is 1.

If you measure the motor amps and voltage ( or use a watt meter) you can determine the power coming into the motor. Subtract about 5% for the power leaving the motor.

The efficiency will depend upon the type and size of pump with large double-suction pumps having the larger efficiencies of around 80 %. Smaller, single suction pumps can have efficiencies of 50-60 %

The TDH includes velocity considerations in the pump inlet and outlet, but these are commonly ignored for most applications because they are small in comparison to the pressure component.

This will be only a rough estimate and will only be as accurate as your measurements and assumptions.

It would also be nice to have the pump curve or the catalog performance table from which a curve could be drawn. But it too will provide an estimate for various reasons having to do with test setups.

The best flow determination is from a calibrated meter run employing an o*****e plate.

Answer 3

*The pressure differential (h) developed by the flow element is measured, and the velocity (V), the volumetric flow (Q) and the mass flow (W) can all be calculated using the following generalized formulas:

V = k*(h/D)^0.5

Q = k*A(h/D)^0.5

W = k*A*(h*D)^0.5

k is the discharge coefficient of the element (which also reflects the units of measurement), A is the cross-sectional area of the pipe's opening, and D is the density of the flowing fluid. The discharge coefficient k is influenced by the Reynolds number and by the "beta ratio," the ratio between the bore diameter of the flow restriction and the inside diameter of the pipe.

Efficiency=shaft horsepower/input power

P=9797Q*H*[ sp. gr.]

Efficiency=9797Q*H*[ sp. gr.]/input power

where Q is in cubic meters per second and H is in meters.

When Q is in liters per second and H is in meters.

P= 9.797Q*H* [sp. gr.]

If you know the efficiency,motor power and sp. gr. , then you can estimate the flow.

Answer 4

there is no way you can do this.  You have to have the pump curve.  You measure the differential pressure p1-p2.  Then look at the pumps unique curve and read the flow rate.  This assumes you have no recirculation and you read pressures across the pump without flow control valves.