Fitted dump valve car slower

[Scootch]

Just fitted my dump valve and the car appears to be slowwer, also noticed when im accelerating the revs r going up and sticking even when i taken my foot off the pedal, summit not quiet right, it was fine before i fitted it , what on earth could cause it to over rev?

[p fandango]

is it a twin piston dump valve? or the only other thing i can think of is the internal spring is too weak so its basically acting as a air leak

[Scootch]

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=150490561912&ssPageName=STRK:MEWNX:IT is this a twin piston dump valve?

[Rnash2002]

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=150490561912&ssPageName=STRK:MEWNX:IT is this a twin piston dump valve?
Ok should be ok comming off another volvo BUT it still could be a single piston one.
Best way ive noticed over the years to tell them apart is the sound it makes when it dumps.
Single seems to make a shhhhhhhhh bit like a bus but the twin will make like a higher pitched note at the end.
If in doubt go to youtube and listen on there,they do make a completely different sound the single and twin.