Types of valves and their usage? 1

[Stuarttait]

Is there a general rule as to when we would use a gate valve as opposed to a butterfly/wafer valve, and same for globe/ball valves and diaphram valves? I appreciate that the material of any type will change depending on the product passing through but are there general guidelines or rules of thumb whereby we would choose one of the four types of valves mentioned (and any other more esoteric type of valve?

Thanks in anticipation?

 

[zdas04]

Stuart,
There was a thread called "Use of Plug Valves" a few days ago that addressed much of this.

The bottom line is several rules of thumb: (1) if a ball valve will work with your temperatures and fluids, it is generally a good choice for on/off operation; (2) Gate valves have a place, but it is usually in on/off service in steam operations where you aren't looking for bubble-tight seals; (3) try not to put an on/off valve design where you will want to throttle; and (4) throttle valves come in a multitude of designs and you will want to take a large dose of cavet emptor before believing valve salesmen (one size really does not fit all). Globe valves have a long history and a definite place, vee-balls are good in moderate temps, diaphram valves have good linearity, etc.

I don't use many butterfly valves any more because I've had a few really bad experiences of trying to dig a broken disk out of piping, but many people have had very good luck with them in a lot of different service. The valve manufacturers claim decent throttlng characteristics, but my experience has been that they pass a lot of flow very early in the valve travel.

Finally, no one in that thread (and no one I've talked to elsewhere) would purposely install a plug valve in any service.

Hope this helps.

David

 

[hero123]

gate valves are straight thru flow valves which provide positive shut-off with minimal drop and flow turbulence. gate valves may be installed without consideration for the direction of flow. They are frequently used for isolation purpose and when sealings in both the directions are required. They shall not be used in a partially open, throttling position as erosion, noise and excessive wear can occur.
Globe valves are primarily used in applications wherea moderate control or regulation of flow is required. it's recommended to be used in the bypass line of a pressure or flow control valve.
Swing check valves are single direction flow valves used to allow unlimited flow in one direction and retain flow in the opposite direction. They are staight thru valve that work automatically. They can also be used in vertical line where the flow is upward under the disc.
Ball valves are straight thru valves which provide positive shut-off with no pressure drop or flow turbulence. They may be installed without consideration of direction of flow. They are receommended to be used in an open or close position only.

 

HI,

You may also benefit by a visit to these site if you want more information regarding vave specifications:

http://www.valvesinternational.co.za/info.htm

and perhaps

http://www.realbusiness.net/hosting/promo/Detail-AltaVista-5.htm

The Ancient One

 

[ralphsare]

posted by zdas04
The bottom line is several rules of thumb: (1) if a ball valve will work with your temperatures and fluids, it is generally a good choice for on/off operation;

ball valves have an equal percentage flow characterisitcs and are therefore suited for control applications.
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Finally, no one in that thread (and no one I've talked to elsewhere) would purposely install a plug valve in any service.

we do. size range from 3 to 6 inch. gear operated. service - general hydrocarbon, fuel gas, contaminated water, tec.
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posted by hero123
gate valves may be installed without consideration for the direction of flow. They are frequently used for isolation purpose and when sealings in both the directions are required.

not frequently but always.

you may want to chekout lyons' valve designers handbook by Jerry Lyons.

 

[zdas04]

Ralph, I've never heard a Ball Valve manufacturer claim that ball valves had "an equal percentage flow characterisitcs and are therefore suited for control applications". I've talked at length to all the major maufacturers and they all say that their ball valves are on/off devices with very poor throttling characteristics comparable to a gate valve. The exotic variants (Vee-ball, zee-ball, etc) are pretty good throttle/control valves with pretty linear flow characteristics, but they are definately not ball valves.

It's interesting that your company prefers plug valves--any details on why a reduced port, high maintenance, non-bubble-tight valve would be preferable to a ball valve? I've always thought of plug valves as the Fiat of valves, and some people love to drive Fiats.

David

 

[ralphsare]

what it means -for a given percentage change in valve opening will produce same percentage change in flow. the chart (% Cv max vc % ball opening) from ball valve mfr such as ktm and jamesbury will make it much clearer.

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our plug valve spec is. A215 body rf 316ss plug, nonlubricated teflon sleeve & diapragm, fire safet to api 607, bolted bonnet, ptfe packing with carbin graphite filled ptfe ring, live loaded packing. that hardly qualify as a fiat. we have it but the number is not much. i would just like to make it a point that if one does not pay attention to the quality of valve purchased, just one valve (fiat or not) in critical service that fail will have an impact in the palnt run time and safety.