Should I put dishwasher tee valve before or after double check valve?

[Essential17]

Hello all.

I’ve just moved into a new build flat that has a waste and electrics for a dishwasher but no cold feed. Site manager said I could add one in myself and I’ve got a washing machine tee valve but not sure where I should put it as there are double check valves on the feeds to the mixer tap (I assume they’ve done that to prevent the mixer tap pushing back into the hot water tank.)

Can I just disconnect the flexible hose from the top of the cold check valve and put the tee in there or would it be better to go before the check valve (or maybe it doesn’t matter?).

I’m also a bit concerned as the flexible hoses going to the tap are already quite high in the cabinet and if I added more height on the cold hose, it would be a bit of a squeeze… but should that be okay?

Some of the other flats in the building have had dishwasher’s pre-installed, so I imagine the plumber just left out the connection here… I just wish I knew they’ve done it in the other flats!

Any advice would be appreciated.

 

[CBW]

Iirc dishwasher and washing machine fills have an air gap, so before the k valve would be ok. After it would probably be ok too.

 

[Hugh Jaleak]

I'd be wary of putting a Tee in above the Check Valves, they may possibly have already caused possible issue by using female ends on a compression fitting, (the tapered end of the compression fitting can cut into the washer, needs to be a flat faced end, or the compression end filed down), currently if it starts to leak you've got some come back against the Builder.

I'd go below, but make sure the flexi isn't under any stress afterwards.

 

[Essential17]

I'd be wary of putting a Tee in above the Check Valves, they may possibly have already caused possible issue by using female ends on a compression fitting, (the tapered end of the compression fitting can cut into the washer, needs to be a flat faced end, or the compression end filed down), currently if it starts to leak you've got some come back against the Builder.

I'd go below, but make sure the flexi isn't under any stress afterwards.

Thanks Hugh. I didn’t realize it would cause an issue but just watched this video which covered the subject quite thoroughly actually!

I knocked on the door of another flat in the building earlier that had the dishwasher pre-installed by the builder and they kindly let me look under their sink. The plumber there had put the dishwasher outlet above the check valve. Makes me wonder if this is the proper way to do it…?

What if I put the tee above the check valve but used a Tap Tail Adaptor to fix what the plumber has done? Or do you still think it would be better to go in below the check valve?