I'm very new to carbon fiber composites, I just want to make some motorcycle parts for myself and friends.  I bought a TA350 pump off amazon, it was about 60 bucks, however I have one issue..

The pump seems to lose  pressure/vacuum when I turn it off.  I thought the pump would be able to maintain the vacuum once I turn it off, but once I kill the pump it will kind of hesitate for a few seconds then almost all the vacuum is lost.  I'm just doing a wet layup with bagging, not infusion so I don't really need the pump to stay on all night. 

Is this normal for most pumps?  I believe I will need a 1 way valve if this is the case, but I'm not sure if the pump is just broken or if some pumps need to be on all the time in order to maintain vacuum.  I gummed up all potential leak spots with bagging tape to make sure the fittings were tight. 

Also I don't know if this is related, but since the pump wasn't holding vacuum, I had a layup with a release ply on top and a breather cloth on top of that, I think that since the bagging was ineffective it caused the release ply to stick to my carbon, I don't know if that sounds correct or if I just did something horribly wrong.  I want to make sure the pump is working first before I attempt my part again. 

Thanks to anyone who can help!

Yeh most pumps not intended for composites processing will flow backwards and lose vacuum when switched off. Just use a ball valve or even just a line clamp to clamp your line while the pump is still on. Your bag needs to be perfectly sealed for this to work though.

Hanaldo is right.  A lot of better quality pumps will have a one way check valve in the system to prevent this vacuum loss and also prevent oil going back up the vacuum line for the same reason.

Even if you had a pump with a check valve, it is still good practice to line clamp the vacuum line for a perfect seal.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant