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bypass v globe valves

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Dougie Swan28/01/2011 20:56:49
269 forum posts
73 photos
Hi,
Can anyone out there tell me the difference between a bypass and globe valve, other then the physical layout of them.
Do they basically do the same thing?
Thanks
Dougie
Geoff Sheppard28/01/2011 21:24:19
80 forum posts
1 photos
Dougie
 
Bypass describes the function of a valve while globe describes its design.
A bypass valve is located on the delivery side of a water pump so that it provides an alternative path (usually back to the tender water tank) so that leaving it open provides a path of least resistance for the water leaving the pump. Closing the valve increases the resistance and causes the water to overcome the boiler pressure and so top up the boiler. Getting the adjustment just right can keep the water level in the boiler constant.
 
A globe valve has a spherical body, so that it has the appearance of a globe. A globe valve can be used as a bypass valve (but not all bypass valves are globe valves, of course).
 
Hope this helps.
 
Regards
 
Geoff
Gray6228/01/2011 21:50:02
1058 forum posts
16 photos
A globe valve is more suited to fluid flow regulation than other valve designs. Globe valves generally have a tapered seat deisgn, the fluid flow is directed downwards onto the valve plug and exits from the seat downwards, This type of valve is most suited to flow regulation.
Another valve design which is generally used where a full bypass is required is a parallel gate valve, these are not suited to fluid flow regulation as when partially closed, the point of wear between the seat and the gate eventually causes leakage.
There are a couple of images in my valves album that illustrate the difference between these two designs.
 
 
Versaboss29/01/2011 11:28:54
512 forum posts
77 photos

An interesting definition, Coalburner.

I suppose your first picture is the globe valve, the second one what you call parallel gate valve (although it seems to consist of a tapered plug).

How do you call in England a valve consisting of a rotating ball with a hole across it? Not a globe valve then?


Greetings, Hansrudolf


Keith Long29/01/2011 11:41:18
883 forum posts
11 photos

Hi Hansrudolf

"How do you call in England a valve consisting of a rotating ball with a hole across it? Not a globe valve then?"

That's usually called a ball valve.

Keith


Nicholas Farr29/01/2011 12:44:42
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3988 forum posts
1799 photos
Hi,
I would call a globe valve, one shaped like a globe, it could have and simple non-return flap or clack mechanism inside, hence the globe shape.
 
In Coalburner's pics, I would call the first one a stop valve, although I think the flow is shown going in the wrong direction, and the second one just a gate valve, and they do normally have a tapered, gate seating into a tapered slidway. I must agree with Coalburner that gate valves do leak after a time of use when they are closed and can only control flow rates in a rough-n-ready manner.
 
Yes Hansrudolf here in the UK they are refered to as an in line ball valve. Not to be confused with the ball operated valve often refered by plumbers in your domestic header tank or toilet cistern.
 
Regards Nick.

Edited By Nicholas Farr on 29/01/2011 13:05:24

Nicholas Farr29/01/2011 17:07:12
avatar
3988 forum posts
1799 photos
Hi,
in typical Blue Peter tradition, a couple I've prepaired ealyer.

This top pic is a stop valve, which can be seen is like that depicted in Coalburners first pic, and on the body of the cut away section is an arrow showing the direction of flow, making it uni-directional.

The bottom pic is a typical gate valve. You may just about make out the wear on one of the edges of the gate and the corrosponding seat edges, which allow them to leak after a while in service. These valves are bi-directional.

 

Regards Nick.

Edited By Nicholas Farr on 29/01/2011 17:11:37

David Haynes17/04/2012 07:56:55
168 forum posts
26 photos

Hi folks,

Can anyone please direct me to drawings for a 1/16 scale globe valve or similar. I want to use it as an injector steam valve on the feed pipe dropping from the turret to the injector.

Thanks in advance,

Dave

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