Gate valves vs. Ball valves.

[Graham]

What are the advantages and disadvantages of gate valves and full-bore Ball valves for mains water, and isolating parts of a CH system.

[Alan Holmes]

A ball valve is to set the level of water in a header tank, a gate valve is use to shut off or allow a flow of water.

Two completely different uses.

Alan

[NikV]

gate valves 'let by' and sometimes drop their 'gate' from the thread -

[Bob Eager]

Not the ball valve he means. The construction is similar to the small service valves one should fit in the feed to things. A rotating spherical shell in a spherical chamber, with holes that rotate in line with the pipes to open, and reverse to close.

To answer the OP, although others will know more...ball valves (in this context) give full flow, as do gate valves. Only ball valves give no flow; gate valves (a) leak a bit and (b) tend to jam. They're also much slower to operate.

[Andy Hall]

Not quite. There is such a thing as a lever ball valve and it is a good choice instead of a gate valve

Ball type float valves are deprecated technology

[Frank Erskine]

A "globe" valve in fact. If there is sediment in the water a globe valve is probably better, since a gate valve may have difficulty seating properly in the presence of sludge.

[meow2222]

given the list of cons mentioned, why r they used?

NT

[Frank Erskine]

They're cheap :-)

[noelogara]

Frank Erskine wrote: > >given the list of cons mentioned, why r they used?

they're crap. Plumbers are old fashioned and dont like to change to easy fittings.

I am referring to flexible hose connections for whb's and flexible waste pipes etc they can be fitted in a few minutes whereas bending copper and cutting and joining pipes makes a big job out of a little one.

I always use the ball valve now for sheer convenience and ease of opening. gate valves almost always are stuck and you never know if they are open or closed.

[Graham]

Thanks for the replies, They mostly confirmed my gut thoughts about the matter.

One follow-up if I may?

What about radiator lockshield (and non-TRV) valves? they are usually, if not always gate valves, and most of mine have weeping steams if not kept fully open. Are gate valves preferred for this application because they are better at controlling the flow i.e. nether fully open nor closed?

[John Rumm]

There is one case where they are useful, and that is when you want to accurately regulate flow (i.e. balancing different zones in CH system). You get better fine control with a gate valve than with a quarter turn ball valve

Yup, for use as service valves they are pants.

[John Rumm]

Yup.

(You may be able to repack the valve gland with grease to stop them weeping when partially open)

[Andy Hall]

Because they always were and plumbers are not renowned for progressive thinking.

[Andy Hall]

Although the delta between these and ball valves is now pretty low....

[Andrew Gabriel]

Actually, they aren't gate valves.

That's a different problem -- the stuffing box wants repacking (might just get away with tightening down the nut, if you can find a compromise where the valve can still be turned, but it stops leaking). Usually, you have to dismantle to clean up the shaft once it's been leaking, as the shaft will have become encrusted which also prevents sealing.

Given how cheap these valves are, it's probably not worth bothering to repair one nowadays.

Gate values are good for controlling flow, where you might want them fully open with minimum pressure drop. They aren't good at sealing off, particularly dirty water. (Generally you do want radiator valves to be able to seal off.)

[Andy Hall]

They tend to be a washer on the end of a plunger which progressively closes the gap to the seat as it goes down - by rotation or being pushed by a pin in the case of a TRV. The range of operation is achieved with quite small movement - about 3-4mm.

If you have weeping valves it is because they are worn out or were crap in the first place. You can go round tightening them and packing them, but IME it doesn't last.

I would have a blitz and replace the lot - it's do-able easily in a morning. Also, I would recommend getting good quality valves. They cost a little more, but when you consider the time and cost of replacing inhibitor after draining to fix one valve, it's worth it.

I did this exercise a few years ago and used Pegler Terrier valves for the lockshields and Drayton TRV4s for the TRVs. For the lockshields you can get them with a drain connection on the radiator side of the valve. This is useful and a lot less messy when taking radiators off for decorating etc.

[Dave Liquorice]

You don't *need* to drain down to change valves, assuming a normal open vented system. Get the plug set for blocking the vent pipe and cold feed and a some old towels to catch the small amount of seepage and away you go.

I'd also shut the valve at the other end of the radiator as well and any zone isolation valves just make sure. When doing this it is vital that you only open the system at one point at a time, *never* two...

[Dave Plowman (News)]

Maybe, but they are *far* more reliable than Torbeck type ones.

[The Natural Philosopher]

IME neither gives full flow.

Ball valves can leak too.

[Christian McArdle]

They're not used in my house. Ball valves (either lever full bore or small bore isolation) or nothing. Even my main stopcock is a full bore lever ball valve.

Christian.