Back Pressure Regulator Behavior
Back Pressure Regulator Behavior
(OP)
A fluid is stored in a tank, and is fed to a particular process through a few hundred feet of pipe using a PD pump. A v-port ball valve at the process controls incoming flow, and the inlet pressure at the ball valve is limited by a back pressure regulator at the storage tank. The set point of the back pressure regulator is equal to the allowable inlet pressure for the ball valve plus anticipated frictional pressure loss in the pipeline. If I close down the ball valve to reduce flow by 98%, will the back pressure regulator be capable of maintaining the same inlet pressure at the ball valve?





RE: Back Pressure Regulator Behavior
I assume the backpressure regulator inlet pipe is also a few hundred feet long, so it will have a lot of frictional pressure drop for the case of 98% of fluid bypassing the ball valve and flowing thru the backpressure regulator. If the backpressure regulator is controlled by a PT located at the ball valve or if teh backpressure inlet pipe is suitably large enough, then I guess it might work OK. If the backpressure valve is controlled by a local pressure sensing tube and its inlet pipe has a large frictional press drop at the max flow, then I guess not.
If the PD pump is constant speed, then one might expect presure and flow pulsations due to the PD pump characteristics, unless you add a compressible chamber or bladder to the piping to snub the pulsations.Alternatively, you can use a VS controller on the PD pump to reduce the performance demands on the backpressure valve, and reduce the size of this valev and its piping.
RE: Back Pressure Regulator Behavior
RE: Back Pressure Regulator Behavior
RE: Back Pressure Regulator Behavior
Tank]--[P]----[BPR]-----------> ------------[V]----
No it will not hold pressure at the V-ball constant. The backpressure regulator will only try to maintain the BPR's inlet pressure equal to its set point. That forms a boundary condition for all downstream pipe flow and that pressure will (should) be constant. Subtract all downstream differential pressures from that. As flow drops with the closure of the v-ball, the frictional pipeline pressure loss will decrease, thus all downstream pressures will tend to increase up to the point where the reduced flow is being imposed (presumedly at the V-ball). The increase will go over the V-ball's allowable inlet pressure, (unless your V-ball 2% open is enough to keep the pressure from building up to that level... something I would NOT count on, so ...
I would call that a safety violation!
Not to mention this is not a good arrangement for a PD pump, unless you want to test its relief valve and/or its drive's strength. I hope it has something that opens to relieve hi discharge pressure back to the tank (or to suction?), or a VSD starts ramping its speed down as a discharge pressure signal goes hi when your regulator begins to close too much.
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Back Pressure Regulator Behavior
RE: Back Pressure Regulator Behavior
Regards
Roy
RE: Back Pressure Regulator Behavior
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain
RE: Back Pressure Regulator Behavior
RE: Back Pressure Regulator Behavior
http://www.plastomatic.com/bprvspr.html
Now take this example by Fairchid, where they call the device a backpressure regulator, but in the technical description they say action is via a "RELIEF VALVE". So unless you give the model number of the specific piece of equipment, things can get confusing.
http://www.finecontrols.co.uk/pdfs/10bpdata.pdf
And this example by Fisher
"Type 63EG Relief Valve [color red]or]/color] Backpressure Regulator"
http://
In any case, if you don't set the relief pressure for the inlet pressure of the V-ball (or whatever the lowest downstram MAOP is), you still have a problem.
http://virtualpipeline.spaces.msn.com
"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain