Restriction Orifice
Restriction Orifice
(OP)
Hi Guys,
I know that restiriction orifice control flow, but do you know how they control pressure?
Is it possible to use RO as pressure regulator? and if so, how is it done?
Bye the way, is any web sites on the internet talking about how RO works? Please let me know if any.
thank you very much
MeEn
I know that restiriction orifice control flow, but do you know how they control pressure?
Is it possible to use RO as pressure regulator? and if so, how is it done?
Bye the way, is any web sites on the internet talking about how RO works? Please let me know if any.
thank you very much
MeEn





RE: Restriction Orifice
ROs are sometimes used as part of a recirc/distribution loop in a system with several "users". For example, they would be installed in a hot glycol distribution system.
The purpose of the RO is to allow the pump to operate within a reasonable part of it's operating curve and to ensure a pressure drop between the supply and return part of the loop.
AN EXAMPLE:
From the circ pump discharge, small taps would go from the main pipe to each user. At the end of the distribution chain, a RO is installed. Then, downstream of the RO, all returns from the users are collected. The system recircs back through a heater and an expansion tank to the pump suction.
Installation of a control valve instead of the RO is another way to achieve the same result.
Hope that this helps........
MJC
RE: Restriction Orifice
Try here
http://www.foxvalve.com/frameset-venturi.html
By the way, the equation is also known as the criticle flow equation.
RE: Restriction Orifice
RE: Restriction Orifice
suggest me the equations to use for calcualting the orifice size for each stage for a given pressure drop and also without causing cavitation of the water.
RE: Restriction Orifice
"dcasto" made a good point in saying that "a Restriction Orifice is simply a control valve in a FIXED (opened) position".
This also implies that any operational flexibility is lost for the sake of minimizing the first cost of your "letdown station". It is a safe bet that at some point in the future use of your system, you will want some control - control that valves would have given you, but which fixed orifices will not.
In any case, if your HP water (117 bar)is at a temperature corresponding to an enthalpy that is greater than saturated liquid enthalpy at 8bar, it will flash (cavitate). Staging the throttling process might be desirable for other reasons, but unless you provide additional cooling as you throttle it will not prevent flashing.
RE: Restriction Orifice
If you post an email address, or drop me an email at testdog2000@yahoo.com, I'll email you a copy of the article.
RE: Restriction Orifice
2) Restriction orifices also do NOT control flow since flow will vary with upstream and downstream pressure.
3) What restriction orifices do is to LIMIT the maximum possible flow through that orifice (and downstream equipment) OR LIMIT the minimum pressure seen by a pump for a given flow. It does this by the designer varing the diameter of the orifice in the metal plate installed in a pipeline. The size of the orifice is determined by the range of operating conditions that can occur across the orifice. Normally you would size the orifice to LIMIT flow based on the maximum possible range in dP or to LIMIT dP based on maximum range in flow .
4) In the example that MJCRONIN addresses, the orifice is actually being used to increase the TDH required for the system so that the system curve intersects the pump curve for the chosen impeller size. Since the TDH developed by the pump is constant, its sometimes easy to say (for this case) that the RO is controlling flow or pressure - But generically - this is an incorrect statement! RO's CAN NOT BY THEMSELVES CONTROL PRESSURE OR FLOW!
The more you learn, the less you are certain of.
RE: Restriction Orifice
This can get interesting, since the multiple orifices can sometimes hurt you versus taking all the drop at an exit expansion. This is because of the additional pipe line dp due to 2-phase flow.
DCasto: I think you meant that a pump produces a constant differential HEAD, not a constant differential PRESSURE.
The more you learn, the less you are certain of.
RE: Restriction Orifice
However, if you are trying to prevent cavitation of the liquid due to the reduced pressure drop at the vena contracta as it passes through the orifice (and the vapor subsequently collapses as pressure is recovered to the bulk downstream pressure), then multiple orifices can help. This is the same principle used in cavitrol trim and other similar valve trims to control cavitation. Basically, the orifices are sized such that the minimum pressure remains above the fluid's vapor pressure.
How practical it is depends to a large amount on the vapor pressure of the inlet fluid compared to the downstream pressure. The closer you are, the more orifices you require.
RE: Restriction Orifice
The more you learn, the less you are certain of.
RE: Restriction Orifice
The article was 'likely' out of Chemical Engineering magazine, perhaps back in the mid 80s, unfortunately, that information didn't make it onto the copy I have. It was written by a pair of engineers working for Ontario Hydro.