You can check to see if it is working by plugging vac port and then take ( I used a biz card) and place it over the holes to see if it would stay in place, It is not going to move a ton, as it only has to open very little to give the relief if you are getting anywhere close to the relief point say 14 hg. with wand on carpet. If it is not working no matter what tm and ALL seals are good WASTE tank it will lug motor way down and may even start to give you belt slippage.
If it is on top of waste tank use a piece of plastic baggie this way you can see if it is getting sucked down into the little holes or not.
I was shocked as when I tested mine it was ALWAYS leaking so I tightened the spring to help it seal better, but if I block my vac port it will climb to @ 16 hg but I never get that on the Legend with wand on the carpet blower just cant pull enough air on the average carpet hoovers around 10-12 hg. CGD gives me about 14-15 hg