Pop tester question

[ghunt]

Couple nights ago I put together my pop tester (made from a jack) and tried to do a test run with it. When I hooked up an injector and pumped it, it didn't build pressure but instead I could see the diesel flowing back up into the fluid reservoir every time I pumped. Why? Is the check valve in the jack body messed up?

 

[icanfixall]

Maybe the pressure relief valve is bad. Did this jack function properly before you made a pop tester out of it. Is the valve that lets the pressure off completely closed..