Stopcock or Gate Valve?

[Fitzroy]

Valves in a fluid system do two jobs:
- isolate the flow
- control the flow

An isolation valve is typically designed to be either open or closed, and to achieve this with the minimum of efforts. Quarter turn ball valves are a great example of this technology.

Control valves are designed to reduce flow and pressure in a controlled way. They typically operate partially open/closed. To enable accurate control they typically go from open to closed over multiple turns of the handle.

Any valve that is open, fully or partially, will only result in a pressure drop when fluids are flowing. Whether you install a stopcock, gate valve, quarter turn ball etc if the valve is open even a fraction then the pressure in your pipe work will equal your supply pressure when there is no flow. You would need a PRV to actively reduce the pressure, this valve monitors the pressure in your system and opens/closes to maintain the pressure at the set pressure. I’ve never seen a PRV in any of the houses I’ve lived in but looking on line they are available.

When the supply pressure is not abnormally high then it can be helpful to run the stopcock partly open/closed, this will reduce the maximum flow rate from the supply, and can help with some dynamic effects like water hammer. A quarter turn ball valve is not a great choice in this situation as a small position change results in a large flow change, so it’s hard to set in a useful position. Additionally the valve will be noisy in operation as it is not designed to operate in this fashion. A regular stopcock, not a gate valve, would be a better choice in this situation. Personally I would go for a quarter turn isolation valve and a traditional stop cock for control.

If you take one thing from this post it’s that a quarter turn ball valve is a poor choice for controlling flow.

Fitz.

 

[Doug B]

In my old house everything after the roof tank had gate valves (which I changed). Someone once did give me reason why stopcocks shouldn't be used on low pressure but I forget what it was. The main reason gate valves fail other than their total jamming is that the groove the "shutter" slides into fills with crud and the valve then fails to close properly. They're a pain in jacksie.

They didn’t use stoptaps on low pressure as back in the day stoptaps had loose jumpers that held the washer & it was the pressure of the water that lifted the washer & jumper as you undid the tap.
For that reason gate valves were used on low pressure both hot & cold where the gate is directly moved as the valve top is turned & when opened gives full flow through the valve without restriction.
I believe it is now acceptable according to the regs to use the quarter turn style valves on water mains but the valves themselves should conform to the regs which if the do will usually have WRAS on them, I doubt some that have been linked to in this thread will.

 

[Spectric]

I believe it is now acceptable according to the regs to use the quarter turn style valves on water mains

They have been for some time, the Pegler ones are also WRAS approved.

 

[Doug B]

They have been for some time, the Pegler ones are also WRAS approved.

Yes I wasn’t sure when it came in but I did notice a while ago that the water board were using quarter turn valves for water main isolation on newly installed mains in the stop tap box on the street

 

[scholar]

+1 for a Sure Stop (even better with a remote switch at a convenient place).

We rely on one of these with incredibly high water pressure - it’s been fitted for about 10 years.

They are WRAS approved as a stopcock.

Cheers

 

[Spectric]

The simplest solution has to be the better option, a quarter turn ball valve is simple with all metal construction apart from the nylon seating and compact. Those sure stop valves are all plastic and only the ones offering remote operation can claim any advantage but I would only use such a valve in addition to a normal shut off valve. Looking at the Surestop it uses tubing for the connections to a remote that suggest it uses a pulse of air to operate, similar to how some of the vehicle central locking systems worked and why I would leave the existing valve in place if it is fully functional.

 

[Doug B]

The simplest solution has to be the better option, a quarter turn ball valve is simple with all metal construction apart from the nylon seating and compact. Those sure stop valves are all plastic and only the ones offering remote operation can claim any advantage but I would only use such a valve in addition to a normal shut off valve. Looking at the Surestop it uses tubing for the connections to a remote that suggest it uses a pulse of air to operate, similar to how some of the vehicle central locking systems worked and why I would leave the existing valve in place if it is fully functional.

Sure Stop isn’t designed as a replacement for the incoming stop tap they say as much In their instructions, it should be fitted after the stop tap but before any branches.
That said Sure Stop are excellent particularly but not exclusively for elderly people who would not only struggle to get down to a stop tap but also to turn a stop tap off. With a flick of the switch the water is isolated which in the case of a leak is the most important thing.

 

[Fergie 307]

The simplest solution has to be the better option, a quarter turn ball valve is simple with all metal construction apart from the nylon seating and compact. Those sure stop valves are all plastic and only the ones offering remote operation can claim any advantage but I would only use such a valve in addition to a normal shut off valve. Looking at the Surestop it uses tubing for the connections to a remote that suggest it uses a pulse of air to operate, similar to how some of the vehicle central locking systems worked and why I would leave the existing valve in place if it is fully functional.

Vehicle central locking and many other systems, often heater controls, work by vacuum provided by the engine. They have quite large storage vessels/accumulators to maintain vacuum when the engine isn't running. Particular favourite with Mercedes, and can be a royal PITA