Ball valve versus gate valve

[sPoNiX]

Doing mods to the central heating...

I notice my central heating has loads of gate valves (The ones with the red handwheels) for isolating various parts of the circuit.

However, the 'fashion' these days seems to be to use service valves (Ball valve with a screwdriver slot).

What are the pros and cons? Why should I use one over the other? (Both are avaivalbe locally at the same price)

Personally I tend to favour the gate valve as the hole through it looks bigger. Any other issues to be aware of?

sponix

[Grunff]

Full bore ball valves are the ones to go for. These have a hole that is the same size as the connected pipe bore, and a flow path that is totally unimpeded. So in the open position, it's the same as having no valve.

[sPoNiX]

More expensive and not available from the sheds..

The gate valve is almost full bore but most "service" valves seem considerably smaller.

Is there any advantage to using a service valve over a gate valve?

sponix

[Dave Liquorice]

Gate valves are notorious for not shutting off completely when they havn't been exercised regularly (fully closed and fully opened at least once/year). Scale or other crud builds up in the grove that the gate slides down and stops it seating properly. Also never leave them wound fully open against the stop, the shaft will jam. Fully open then close 1/4 to 1/2 a turn.

You can get "full flow" ball valves.

[Grunff]

But well worth it imho. All plumbers merchants carry them, as do screwfix, toolstation, bes etc.

Service valves are smaller in size, and also 1/4 turn. These are both 'advantages', but not huge ones.

[Christian McArdle]

I would use neither. Gate valves are unreliable. Service valves are small bore. I use full bore lever valves.

Christian.

[Dave Plowman (News)]

For maintenance purposes yes. Old gate valves never shut off completely. Although this might only be in a hard water area.

[Aidan]

When I were a lad, gate valves were what we used before ball valves became commonly available.

Gate valves were used in preference to globe valves (stopcock/screwdown-tap types) on pumped circuits because they offered little resistance to the flow. Their disadvantage was that they often failed to fully isolate.

That's all now history, use full-bore ball valves.

Service valves have a reduced bore and are intended for use on water supply systems where the increased resistance is of little concern. Use full-bore ball valves on pumped heating systems.

The gate valves' glands are liable to start dripping if you do operate them after a long time. The glands are probably packed with asbestos fibre material. The 15mm gate valves must be worth at least 10p as scrap.

[John Rumm]

Wot the others said, plus, gate valves have an endearing little habbit of getting stuck, then the shaft breaking internally as you go to open them. The nett result being that it feels like you just undid a tight valve, only you didn't!

DAMHIK

[sPoNiX]

Unfortunately, I don't have lever ball valves available...only 'service' ball valves or gate valves.

I'm gonna use a gate valve methinks as there are already other gate valves in the system that seem to work fine.

sponix

[Andy Hall]

B&Q usually have a few, but not at the best prices. If you look at BES, Screwfix,... they are reasonably priced, but not as low as service valves.

Service valves are not a good idea for heating because they impede the flow too much. Their best application is for isolating taps and toilets on mains pressure supplies. In heating, the only useful application I can think of for service valves is for a bypass.

Compared with gate valves, apart from also being full bore they:

- shut off flow completely

- don't leak around the spindle

- don't stick with heat or scaling.

[Pete C]

Hi,

They're best in vertical pipes where sediment can't collect in the bottom, in any case closing them while there is some flow might help pull through any that has collected in them.

cheers, Pete.