For flow control which valve is appropiate

[sridhar1312]

For flow control at the outlet of chiller and condenser and at the inlet of cooling tower cells we have been using Globe valve or Balancing valves to set the correct flow across respective equipments.
One of the vendor wants to use butterfly valve as isolation as well as flow control, Is it correct.

 

[ScottyUK]

Butterfly valves make lousy control valves because of the desperately non-linear response. The only reason to use one as a control valve is to minimise cost.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[katmar]

There are millions of butterfly valves around the world performing this type of duty very well. As long as the valve sizing is correct and it is not running near full open (where a butterfly valve has too high a gain). Tell your vendor that you are concerned and ask for a guarantee and a copy of the sizing calculation. The quality of self-tuning electronic controllers and valve positioners is so different from 2 or 3 decades ago that the old rules of thumb like "don't use butterfly valves for control" simply do not apply any more. Cooling water, steam and air valves are often large and it is just crazy to install an expensive monster globe valve where a butterfly will perform more than adequately.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[zdas04]

While it is often done, it really isn't a great idea. Control valves tend to be lousy block valves and vice versa. If I'm trying to control something I chose a valve with decent linerarity. Butterfly valves do not have this. If I'm trying to isolate flow I use a valve with good sealing characteristics, and butterfly valves don't really have this either.

The only reason to use a butterfly valve for any service is installation cost. I find that to be a very short sighted reason to pick equipment since the lowest installation cost is often the highest life-cycle cost when you factor in the cost of lost production while replacing a valve or the cost of extraordinary isolation techniques like "freeze stopple" to get isolation to replace one whos disk has come off.

David

 

[JLSeagull]

If using butterfly valves, common in NPS 10 and larger lines, only permit high performance or triple offset butterfly valves not conventional butterfly valves.

 

[BigInch]

Not all controls need strictly linear curves. If you can't use a butterfly valve for ON/OFF, which you shouldn't, what can you use them for. As Katmar says, if the calcs work, it should do fine.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

Exactly. "If you can't use a butterfly valve for ON/OFF ... what can you use them for?" I say they fit into the same category as plug valves. I never call them out and frequently solve field problems by replacing them with other technologies. Until you get above about 30-inch in low pressure service there are always better valves. Even in larger lines there are usually more effective options, but the cost/benefit can be a bit obscure.

David

 

[katmar]

It's a matter of horses for courses. In the world of zdas04 where he is dealing with enormous volumes of highly flammable gases under extreme pressure different valves are required from when you are dealing with cooling water. And not only different valves - the piping itself, the gaskets, the bolts and even the paint will be a totally different class.

I have seen butterfly valves used successfully for isolation and control on steam. But this is 30 psig steam in distilleries. You would not use this type of valve as the crown valve on a 1200 psig power boiler, or the control valve to a turbine. But those are not the applications involved in the original question.

I cannot ever remember seeing a globe valve on a cooling water duty. In the old days we used gates, and now we use butterflies.

There is no "one size fits all" in the application of valves and every instance has to be treated on its merits. Perhaps sridhar's application is a very arduous one, but on the face of it I would say it sounds like the correct place to use a butterfly valve.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[zdas04]

I worked in a steam plant in the 70's (built in the 50's) that had rising stem gate valves on sea cocks to the condensers and on the condenser side of the gate valves the smaller lines for lube-oil coolers had gate valves at the trunk. Right at the cooler outlets we had globe valves to adjust lube oil temp (if I was designing the system I operated I would put an automated valve on the cooler outlet, but operators don't get to make those sorts of decisions). That sounds similar to the OP's question. This was a ship so the temperature of the cooling water could change dramatically very rapidly so we had to watch those temps really closely. I would have hated to cross the boundary into the Japanese Current with a butterfly valve for control.

On land based steam plants the issues are probably less dynamic and a butterfly valve might be the most cost effective answer, I'd have to run the life cycle economics to convince myself of that.

David

 

[dcasto]

The last plant I worked in had 45,000 gpm of cooling water in just 1 plant. We used butterfly valves exclusively to isolate and throttle the water to each exchanger.

Since you should never have any one of the butterfly valves more than 45% closed, the Cv range is perfect. What happens is that during the year, the operators adjust valves to balance loads and every valve eventually all wind up being partially closed. SO, you go back and reset them open and close just those that require lower flow.

A leaking butterfly on a water system is not a concern. We would slide a paddle in on the exchanger if we needed absolute shut off.

 

[whammett]

I agree with katmar, under medium to high PSI requirements on the outlet of a chiller/condenser, I would never use a STANDARD butterfly valve. However, as JLSeagull states, high performance buterfly valves are a completely different beast. It is also A LOT cheaper to get a FO or FC butterfly valve, as most globe valves are fail stationary.

"I came, I saw, I made it better."
-Ode to Industrial Engineers
Will ChevronTexaco Corp.