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IP return line check valve... the little glass ball


New member
Suffolk, VA
I'd like to dedicate this thread to the discussion of the mysterious little glass ball in the check valve on the top of the IP cover.

I did some searches and didn't find one good thread about it. But lots of miss information and various opinions through out many threads.

To start this off I'd like to offer what little experience I've had with it.

First, I understand it's part of a check valve (a spring pushes on the ball to close it when not much fuel pressure is there) that is supposed to keep the fuel from syphoning out of the IP when the truck is turned off. I think it is a more important feature with a stock mech pump than with the electric pumps that start pumping once the key is on (like what I put in my trucks).

Second, some people will take a small punch and break them out so that they can't clog (or to fix a clog) and stop the necessary flow out of the IP and into the return system. But I understand the IP is designed to close the return through them down at high RPMs inorder to guarantee sufficient fuel to the injectors.

I've robbed them from my old IP's that I've sent in for rebuild and keep a couple on the shelf for just that reason... one them was cracked (had to hold it up to the light and look through it carefully to see it) so I busted the ball out and use it for trouble shooting and also on my truck that seems harder to prime.

To function check stock ones, I've used a can of WD40 with a spray straw and made sure it flowed freely one way but not the other.

To see how well it is working, i've always placed a piece of clear tube between it and the return line. These hoses aren't rated for diesel (what clear line is?), so with the exposure to diesel and heat they become brittle. I change them every 6 months to a year or so. This is recommended in the Haynes Diesel Techbook

When changing fuel filters (I have an electric pump) sometimes they keep closed and keep air in the IP. This is frustrating, but once the truck is running they seem to open and let the air purge out. The truck runs rough until the air is totally out of the IP. It seemes to me that with my electric fuel pump, and the truck I put a busted out glass ball return fitting on, it primes easier.

Please add your observations and comments!


Active member
Marcy, NY
Does anyone have a photo of this mysterious valve and it's location?

Is it worth replacing as a matter of preventative maintenance?

(and sorry, I know it's an old thread)
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