Orifice Plate Permanent Pipe Losses
Orifice Plate Permanent Pipe Losses
(OP)
I am designing an orifice plate to reduce the pressure in a system. I know how to use orifice plates to measure flow via differential pressure, but I do not know how to calculate the losses in head pressure in a system due to this constriction. Anybody know of some resources?
Here are my givens.
Fluid- Water
Pressure- High side 2800 psi
Pipe diameter- 3.438 in
Desired pressure downstream- 950 psi
Find Orifice diameter
Thanks for your help
jnb
Here are my givens.
Fluid- Water
Pressure- High side 2800 psi
Pipe diameter- 3.438 in
Desired pressure downstream- 950 psi
Find Orifice diameter
Thanks for your help
jnb





RE: Orifice Plate Permanent Pipe Losses
RE: Orifice Plate Permanent Pipe Losses
RE: Orifice Plate Permanent Pipe Losses
You have not specified a flowrate.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: Orifice Plate Permanent Pipe Losses
RE: Orifice Plate Permanent Pipe Losses
These numbers are for an API 14.3 plate. If you increase the thickness of the restriction, the permanant pressure drop increases until it approaches 100% for all choke sizes at about 3 pipe diameters.
David
RE: Orifice Plate Permanent Pipe Losses
RE: Orifice Plate Permanent Pipe Losses
if this is a pump by pass, the pump manufacturer can sort you out.
RE: Orifice Plate Permanent Pipe Losses
Approach 1: Use equations for "pipe-taps".
Approach 2: Use equations for "flange taps" (or close up taps) and correct dPcloseup to get to dPpermanent.
Approach 3: Use K value equations (from Hooper for example).
I have always used Approach 1 or 2 and agree with JLSeagull that Spink and Miller is the best reference for this.
RE: Orifice Plate Permanent Pipe Losses
Thanks a lot for helping me out with this. The first post in response made me feel like I really missed something in college. Orifice plates are typically designed to measure flow and typically the only place of concern with pressure is before the plate and within the vena contracta that the plate produces. They are not typically used in the fashion that I described, but can be. I am part of a start up engineering team and we need to drop the pressure to one of the end users during a system flush.
RE: Orifice Plate Permanent Pipe Losses
Paul
www.ostand.com
RE: Orifice Plate Permanent Pipe Losses
I believe that RO = reducing orifice
RE: Orifice Plate Permanent Pipe Losses
RE: Orifice Plate Permanent Pipe Losses
http://www.tercom.it/index_file/Page681.htm
http://www.int-instrument.it/Inglese/Pagina18.htm
RE: Orifice Plate Permanent Pipe Losses
Converts potential energy to kinetic energy and destroys the kinetic energy.
calculate the area of flow through the orifice (= orifice area 8 contraction coefficient (0.65 say for blunt edge) calculate the velocity through the contracted orifice.
Head loss = (Velocity through the orifice - downstream pipe velocity) ^2/2g (SI units)
RE: Orifice Plate Permanent Pipe Losses
Converts potential energy to kinetic energy and destroys the kinetic energy.
calculate the area of flow through the orifice (= orifice area x contraction coefficient (0.65 say for blunt edge) calculate the velocity through the contracted orifice.
Head loss = (Velocity through the orifice - downstream pipe velocity) ^2/2g (SI units)
RE: Orifice Plate Permanent Pipe Losses
RE: Orifice Plate Permanent Pipe Losses
a) only works correctly for one single flowrate
b) severe erosion downstream of the orifice and at orifice is likely- in such applications ceramic orifices have been used, but a much better fixed restriction is to use a small diameter stainless steel capilary tube.
c) prediction of flow will be tough if flashing or cavitation occurs. If teh pressure in the vena contracta drops below saturation pressure, steam bubbles will form and choke of the flow, then collapse at soundpseed after pressure recovery and severely erode via cavitation. Again, a SS capilary tube obviates this issue.
If the process conditons are expected to cahnge ( flowrte, fluid temp required pressure), then one should use an anticavitation control valve.
RE: Orifice Plate Permanent Pipe Losses
I've seen similar problems, the up and downstream pressures are fixed by other control systems. If you needed to maintain a minimum flow on a pump with the given conditions, you size the orifice to do maintain the m inimum flow. Yes it appears to be a waste of energy, but, it depends. Small injection systems where min flow is 5 gpm, that wouldn't be much of a loss and the capital for an RO is almost zero compared to an elaborate valve.
Another place is where you have a blow down systen durin an upset. Example: There is a 2" ball valve that vents to VRU to get the material out of the system. We didn't want to flow more than 15,000 lbs/hr. Plug in the up/down stream pressures, max flow, bingo a .375 plate. Its only used in an emergency, so worrying about errosion isn't a concern. we had this type arrangement all over the plant.
RE: Orifice Plate Permanent Pipe Losses
RE: Orifice Plate Permanent Pipe Losses
Reinventing the wheel is OK- we've all seen it before.
One can use a series of orifices, but you still need to confirm the pressure at the vena contracta of tehlast orifice is higher than saturation pressure for teh case of the highest flow and highest fluid inlet temperature in order to avoid cavitation.
The problem outlined is a common problem with power plants- either boiler feed pump recirc or older supercritical boiler startup systems - the cadilac fix that preserves plant avaiability is to use capilary tubes or an anticav valve. In the case of a $1billion USD power plant , one can pay the extra money to ensure availability. If its an agircultural ditch worth $50 K, maybe not.