Butterfly Valves in Pump Suction
Butterfly Valves in Pump Suction
(OP)
There is a major push to install remote isolation valves on the suction lines to many of our pumps. This is necessary for safety. In order to try and hold costs down, the piping project managers are pushing hard to get me to accept butterfly valves for the larger sizes. These valves are sometimes installed in the common suction line before it tees off to the two pumps. However, often the isolation valve is located just downstream of the existing gate valve used for pump isolation. This would place the butterfly valve within 2 or 3 pipe diameters of the suction flange. I know this is a bad idea. I know it will reduce NPSH margin, increase turbulence and encourage vibration. What I am looking for is some real world experience from other engineers that I can use as a basis to resist this effort. Has anyone had a reliable pump turn into a "bad-actor" after a butterfly valve was installed? Has anyone been forced to go back at substantial expense and replace butterfly valves in order to address chronic reliability problems? Any examples or experiences related will be greatly appreciated.





RE: Butterfly Valves in Pump Suction
What do the valve manufacturers have to say?
Always a problem to go against your beter judgement but you have been around for long enough to understand the need to document your apprehension of using butterfly valves in this installation.
RE: Butterfly Valves in Pump Suction
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Butterfly Valves in Pump Suction
The data (all maximum values) for a rough idea
Pump flowrate - 300 m3/hr
Water temperature - 320C
Suction Pipe - 10"
Valve to suction flange - 30"
RE: Butterfly Valves in Pump Suction
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
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RE: Butterfly Valves in Pump Suction
RE: Butterfly Valves in Pump Suction
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Butterfly Valves in Pump Suction
1. Evaluate the NPSH margin taking into account the additional head loss imposed by the valve. With the valve installed, we still have to satisfy our specifications for NPSH margin.
2. Place the valve back as far away from the pump as possible. It is preferable to install a single valve in the common line to both pumps. This way any turbulence or maldistribution of velocity would have equalized by the time the flow reaches the pumps.
I would prefer to say "NO Butterfly valves" within 10 pipe diameters as a firm rule for the project. But I don't know if they will accept the higher cost of piping changes or ball valves without some justification. My engineering judgment is that the butterfly valves are a bad idea and may cause a reduction in pump reliability in some cases. But proof is hard to come by. API RP-686 states that no fittings (valve, reducer, elbow, etc.) should be located within 5 pipe diameters of the suction of a pump. But we have pumps all over the refinery (100's of them) that have an eccentric reducer and elbow right up against the suction flange. And most of these pumps run well. But that does not prove that it is a good idea to pipe them that way.
I was hoping that someone had gone down the path that I am being pushed down and that I could benefit from their hard learned lesson.
RE: Butterfly Valves in Pump Suction
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Butterfly Valves in Pump Suction
"Find me someone who is dumb enough to admit that (what I'm pushing you to do against your better judgement) had a bad outcome ... or your tenure here will have a bad outcome", or words to that effect.
Do they teach that in business school?
Mike Halloran
Pembroke Pines, FL, USA
RE: Butterfly Valves in Pump Suction
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Butterfly Valves in Pump Suction
We have lots of posiseal butterfly valves that ESD to protect our equipment, and yes, we use them to isolate the same equipment. The service is cryogenic gas at 800 psig. If the equipment is take out of service, a blind flange is attached. It takes two sets of flanges, one for the valve to be set betwen, the other to blind the valve. Yes, we have a small gas leak going by the seals of the butterfly valve that we must deal with. If you can not afford some leakage, then go to a ball valve or DBB gate.
RE: Butterfly Valves in Pump Suction
2. Place the valve back as far away from the pump as possible. It is preferable to install a single valve in the common line to both pumps. This way any turbulence or maldistribution of velocity would have equalized by the time the flow reaches the pumps."
I would evalualte point 1. and make a recommendation on the valve location based on your own judgement and would not be prepared to sign-off an any other recommendation.
If the valves are too close and cause problems - you have a problem. If installed 10 pipe diameters upstream of the pump inlet and everything is OK the additional costs do not become a consideration.
RE: Butterfly Valves in Pump Suction
For my company valves that do not meet "fire-safe" get fire proof insulatation and/or water spray per NFPA, to ensure fire does not freeze the valve or actuator. Rather than leave it to human factors (to actuate the valve), our valves have fail closed actuators with "fusible links" (a piece of pressurized tubing" that melts off releasing the pressure when exposed to fire.)
Whether the valves will cause flow disturbances depends on the suction energy. If there is a high suction energy and not enough suction head or straight pipe, caviation can occur. I will try to get the information I have gathered tomorrow & post again tomorrow night.
G
RE: Butterfly Valves in Pump Suction
Where you can, use the butterfly valves to your advantage. Often pumps can use a little bias in the suction to offset piping errors or flow patterns. A butterfly valve passes full flow long before it is 100% open, so if some can be stroked so that they give a little 'tweak' in the direction that is beneficial to the pump, then set it up that way. Remember that butterfly valve shafts don't necessarily have to be vertical either. That 'tweak' might be to compensate for a concentric reducer that is not properly placed. So put them horizontal or in what ever position helps the pump the most.
If you are going to be made to do it, then do it your way.
rmw
RE: Butterfly Valves in Pump Suction
BigInch
-born in the trenches.
http://virtualpipeline.spaces.msn.com
RE: Butterfly Valves in Pump Suction
RE: Butterfly Valves in Pump Suction
RE: Butterfly Valves in Pump Suction
RE: Butterfly Valves in Pump Suction
Mark McLean
RE: Butterfly Valves in Pump Suction
One of the most significant problems with butterfly valves is their propensity to make messy flow distributions worse. (If the flow pattern is not distorted, a fully opened butterfly valve will add relatively little distortion to the flow.) The main precaution that I would want to take is to pay close attention to nature and configuration of flow disturbing elements leading into the butterfly valve.
Although a butterfly valve is usually considered as passing full flow when it is well short of being fully opened, it will serve as a distoring element for the downstream flow pattern for any position other than fully open.
For example, if the butterfly valve must be located downstream from an elbow, I would make sure that the shaft of the butterfly valve is aligned parallel to the pipe leading into the elbow, that the butterfly is truly aligned along the pipe axis when fully open, and that the valve is located as close to the elbow as may be practical. This would minimize the influence of the butterfly valve on the flow pattern.
The reasoning for this is as follows. An elbow tends to produce opposing symmetric swirl patterns in the flow leaving the elbow. This alignment of the butterfly minimizes its potential influence when fully opened. Any other orientation of the butterfly would tend to augment and distort the turbulence in the flow downstream from the valve. Locating the butterfly valve close to the elbow maximizes the length of straight pipe after the valve to allow maximum calming of the flow pattern before the pump.