Feed Water Pump

is it feed head at the inlet at 1.5 bar, and what do you want to increase it to.

Do you want to increase the pressure, or the flow?

What size is the piping, before and after the pump.

Are there gauges in the system?

Flow meters?

Definitely insufficient information for a coherent reply. Provide full details, and the size of the boiler it is attached to (in units of lbs steam/hr).

Dear Mr.aneeslarik,

Pl. check the Name Plate Details - where Delvery Pressure and NPSH required.

You have mentioned 1.5 bar and 2.5 bar - I am of the opinion that this pressure could be NPSH.

To calculate the NPSH, we have to know the Feed Water Temp. You have not mentioned the temp.

By knowing the the speed of the pump and the Diametre of the impeller at the tip and at the eye, we can calculate the pressure. Based on the dia and speed as referred above, we have to caculate the Velocity.

Let V1 be the Velocity at the tip and V2 be the Velocity at the eye, in Metres/Sec., Pressure in Metres is caculated by the Equation

((V1)^2 - (V2)^2))/2 x G = (HEAD)^2 where G is accln.due to gravity which is 9.81 M/Sec^2

Take the Sq. Root for the Head^2. That will be the Pressure in Metres, devide this by 10.75 and you will get pressure in Kg/cm^2 and you multiply this by 0.981 and you will get pressure in bar.

DHAYANANDHAN.S

Pretty good one, old chap. However, we still do not know if this is NPSH to the boiler feed-water pump, or is the actual low-pressure boiler steam head pressure. For all I know, this could be a small feed/grist mill plant, a laundry, etc.

There are some issues here that concern me.

Is the pump centrifugal because there is a difference between how a discharge pressure is delivered between a centrifugal and a reciprocating pump.

A reciprocating pump will generate enough pressure to overcome the losses in the discharge system. To get an increase in pressure at the pump just increase the pressure at the end point of the circuit.

From your other comments I think this is a centrif because you mention putting in a motor of twice the capacity to get the performance you need. This worries me. A bigger motor has more power and torque and this may exceed the strength of the driveshaft so there is a risk of damaging the pump. If the pump was supplied with the correct motor and should have delivered 2.5 bar then there may be other issues which you have not identified.

A centrif delivers a head (measured in metres of fluid). If the density of your current fluid is lower than that in original design this will reduce the pressure in bar that is delivered.

Similarly if the suction pressure (or static head) are now reduced from the original design this will also explain the reduced discharge pressure.

A centrif has an operating curve of head against flow so it is possible that although it was designed for 2.5 bar at a specific flow if you are now operating at a higher flow the pump will only deliver a lower head. (The pump curve should be part of the vendor information supplied and you will see how it slopes down giving lower head at higher flows)

Has the NPSH been investigated. If the fluid being pumped is warmer than originally designed (ie closer to its boiling point) or at a lower level the NPSH may be reduced and there may be cavitation in the pump which among other things would reduce the performance. As this causes significant damage to impellors this must be investigated.

These issues should have been investigated before the brute solution of a bigger motor.