Check Valve or 'Double' check valve?

[ingram]

I need to install a check valve ( for a water softener installation).

Screwfix list Check Valve and Double Check Valve and the local stores seem only to stock 'Double Check Valve'.

The 'Doubles' have a small screw in the side of them:
Does the 'Double' simply have two valves in it instead of one?

If so why?
What is the small hex head screw for?

Thanks in advance chaps.

Harvey

 

[seco services]

yep

 

[Balenza]

Double check valves may be used in most cases of Class 2 and 3 risks in which case it is suitable for your water softner.
The test cock in the middle of the valve is in order to test whether or not the valve downstream of the test cock is effective.

 

[ingram]

Thanks; question answered; Harvey happy

H