I built a pop tester with a bottle jack from the many fine posts on the site, but am having a problem with it. I used a new bottle jack, but it was an inexpensive one from Harbor Freight. The bottle jack appeared to work before I modified it for use in the pop tester, but I'm afraid I didn't try lifting anything heavy with it to be sure. When I pump the the jack, diesel flows through the system and comes out the injector end. I pump enough that there appears no air is left in the system. When I attach an injector to the end, the pump won't put out enough pressure to get near the popping point, and it won't hold the pressure that it does achieve. I took it apart and inspected it as well as I could and it seemed to look OK inside; nothing clogging or a spring hanging up or whatever.

Is there some way to determine if the pump itself is just defective, or does the way it's working prove that it is? Maybe some priming or purging of air in the pump that I'm not doing?

Thanks for any ideas.

The pump is very likely leaking internally from the high pressure side to the reservoir side. It's kind of tricky and very important to get things sealed up properly. You want to make sure that you've plugged the little vent hole that is designed to keep the pump from popping the lift cylinder out of the jack (in the jack cylinder) and the 1/8" or so hole in the jack nut. Either of these will dump diesel under pressure back into the reservoir. You will also need to ensure that the jack nut is sealed to the jack cylinder. I used a heavy wrap of teflon tape the second time I attempted to build one. An alternative way to go is to seal the threads with JB weld. Also make sure that you have good welds on the jack nut where you weld on your fitting that goes to the T-fitting with the gauge and pressure line.

I messed up my first attempt by not getting a good seal on the jack cylinder to jack nut with precisely the same symptoms you report.

I've still got some custom 1/4NPT-MB hardline fittings if anyone is building a pop tester and is looking for an easy way to get from one to the other in one step.

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Thanks!,
When I can check this out, I'll report back.

where are you guys placing the filter on these home built testers?

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Brian
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I put mine between the diesel reservoir and the intake on the side of the pump.

what are the pressure ratings on the brass parts you are using in your tester? they look like standard plumbing fittings ~150psi... scary!

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vstech,

Why do you think that standard plumbing fittings are rated only 150 psi? Small fittings can hold enormous pressures. I recall that 1/8" Swagelock fittings are rated ~20,000 psi. Still, I would prefer steel to brass. One wouldn't want a jet of diesel in the eye or throat. Always wear a face shield when using a pop tester.

Re filter, a small high-pressure "rock-catcher" type filter screen would be good after the pump. I'll look around for such for the tester I plan to build.