Hi Pipers
first post on this forum
what the use of BPV(Back Pressure Valve ) in Minimum Flow Lines of Feedwater Pump Piping to Feedwater Tank.
if we are using BPV still we need of ORIFICE PLATE ?
Regards
Sunil Garg

The answer could be YES or NO depending on what the Process Engineer is trying to do with the whole system.

a) A"BPV controls the Pressure, so is the Process Engineer trying to control the Pressure?

b) An Orifice Flange/Plate measures the Flow, so is the Process Engineer trying to measure the Flow?

You do not or use use an Orifice Plate/run to measure Pressure.

If the Process Engineer shows both the BPV and the Orifice Run on the P&ID you, as a piper are obligated to follow the P&ID and install both.

A BPV in the minimum flow piping is to protect the pump in case the pressure of feedwater tank increase when pump in stop condition.
And when BPV is present there is no need to have an orifice plate. For process requirement we don't measure flow in minimum flow line.

hi n.mech
thanx for quick reply
as u said there is no need of putting orifice plate in minimum flow lines ....but the P&ID shows the orifice plate in the min. flow lines whether these min. flow lines is of main feedwater pumps or even with the preheating pump's Min. flow lines ....
btw can you brief the use of min. flow lines for a pump
Regards
SG

If its given is P & ID then ask the designer for the reason and let me know also.

btw can you brief the use of min. flow lines for a pump

Feed water pumps are mostly high pressure pumps and its motor requires higher starting torque. So while starting the pump its discharge valve is kept close to avoid tripping of motor. In that condition minimum flow line is useful to maintain flow and pressure.

hi N.mech
ur answer seems to me incomplete.....
the way u have described the function of minimum flow lines at the satrt of pumps remind me of the term priming isn't it?
to me minimum flow lines is to maintain a minimum flow from the pump so we dont need of frequently off and on the pump on load variations .
it is too costly and cumbersome to restart the pump again n again .
so when the load is low means need to send less water in HRSG we close the discharge line valve
and the flow goes from minmum flow lines to feedwater tank
Correct me if i am wrong!
Regards
SG

This is sounding a lot more like process discussion than piping!
SG haven't you given the answer yourself?
The RO's when they are not used to transmit the flow rate, are used to reduce / regulate flow. Therein lies your answer.
Regards,

Hi Sk,

Minimum recirculation line has nothing to do with priming though it does provides a faster FW pump startup. The priming is automatically obtained as the Deaerator is in the higher level which provides flooded suction. The minimum recirculation line is provided with ARC (automatic recirculation valve) so that the Feedwater Pump operate within stable region of the HQ curve. This is entirely for the safety of the pump.
Orifice is provided for minimum flow line for flow measurement. The flow signal shall be used to adjust the discharge control valve of the FW pump. There is a considerable pressure drop also. Normally the Orifice is at the downstream of the ARC.

Cheers

Sudipto