Double union ball valves have both advantages and disadvantages – figuring out where you need the valve in your pipe system and what kind of control you want to have over the flow will help you decide whether a double union ball valve is the right choice for you.
A double union ball valve has, as implied, two unions on it – one on either side. The unions enable the valve to be unscrewed and removed from the pipeline, where it can be serviced or checked to see whether it's blocked, and then easily put back in the pipeline where the unions can get screwed back on. This means that to get to your valve and service it, you won’t have to worry about cutting your pipe. It also means that returning your valve to your pipe system is a fast process and won’t keep your system down for long.
The main advantage of a double union ball valve is that it has a full-bore flow all the way through. This means there is nothing to catch any debris that might be coming down in the water or fluid. Therefore, it is highly unlikely to get blocked.
An alternative to a double union ball valve, which still has the same benefits of a full-bore flow, is a single union ball valve. However, a single union ball valve only has a union on one side of it. Due to this, a single union ball valve should be used at the end of a pipeline rather than in the middle of a system. If it was used in the middle of a pipe system and you had a problem with the valve, the only way to remove it would be to cut the pipe on one side and then unscrew the union. You would then be left with having to glue a fitting onto pipe. This means your system would be down for a lot longer. That's why we use double union ball valves in a system, and single union ball valves at the end of a system.
While ball valves have their advantages, they are not easy to control. There is only a quarter turn on the valve between fully open and fully closed, which means it is very hard to get a fine control of flow. They're great if you want a fully open flow, a fully closed flow, or perhaps somewhere around a half-flow. But if you want finer control than that, you are much better using a gate valve, which has around eight turns between fully open and fully closed. Gate valves enable you to get fine control on the valve and fine control of the flow.
All our ball valves are pressure tested to 10 bar pressure. They are also all wet tested at the factory before they come to us, so if you find a tiny bit of water or fluid in and around the valve when you take the unions off, that doesn't mean it's been used on someone else's system, it means it's been wet tested at the factory and is therefore in perfect working condition!