Dump valve behaviour

[Dave_M]

Evening all

When I had my BT escort idling at the weekend with the bonnet open I noticed a hissing sound coming from the Bailey vent to atmos dump valve. The piston was fully open and the engine was sucking in (unfiltered) air though the DV. As soon as I blipped the throttle I could see the piston close and the hiss stopped until the inlet went under vacuum again.

I assume this behaviour isn't right - is my dv knackered? I've got a recirc valve which I haven't got round to fitting - might try popping that on.

Cheers
Dave

[twin turbo]

its how they are. the vacum lifts the piston

[Dave_M]

So do all vent to atmosphere dv's suck in unfiltered air? This just seems wrong to me. I know they open based on vacuum in the inlet plenum but would have thought there'd be some Spring resistance so that there had to be positive boost pressure in the pipe work for the piston to open.

Dave

[cossiedavid]

Fit a spec-r one they have a filter around them

[Adamski]

No its as been said the positive pressure shuts the valve and when you let off the vacuum pulls the valve open to release the pressure. There is 2 types of Bailey tho the single and twin piston.

[Barney Gumble]

I've got a forge one with a filter on it.

[Dave_M]

Cheers all. I guess my best solution is to fit the recirc one I bought..

Dave

[twin turbo]

or just remove it

its no big problem if not driving on gravel or very dirty area, With the open dump, they have been used for 30years

[Jase]

I had exactly the same, like Adamski said, you want the twin piston type and that solves the problem with a smaller less highly sprung piston/stopper.

As its before the throttle housing, it doesn't affect the car on tick over and as soon as you rev it the piston closes so it's unlikely to cause any issues, but I was exactly the same as you, so I sold mine and bought a twin piston Forge.