Fuel line check valve

I have a 1989 Viking 35 sportfish. I've been dealing with a generator fuel starvation/priming issue since I got the boat 3 years ago. I solved a variety of problems with the genset and when I can keep the fuel flowing it runs and performs great, but given how hard it's been to prime the fuel line and keep it that way I decided to pull the fuel pickup and check the anti siphon valve for proper operation. For reference it's about 15-20' from tank to genset filters.

It was hard to get the fittings apart, and at this point I have not got the pickup tube out, but what I found was a check valve, not an anti siphon valve. Perhaps they solve the same issue. The check valve being so close to tank is being used to solve just the issue I'm having, the fuel draining back to the tank and priming issues given the length of hose run.

Anyway, the check valve appeared to be very difficult to operate. I assumed it was junk. But after a thorough cleaning, it still appears very stiff, but maybe I don't have an appreciation of what is needed to generate 2psi for the cracking pressure of this valve by blowing through it. The electric fuel pump is rated for 2-5psi, so I think it's having a hard time keeping the valve open. If I help it get the flow going with a primer level, it will keep flowing and running. Additionally, and I'm told this can be done but isn't as common, the check valve is installed on the suction side of the pump, with the valve at the tank and the fuel pump mounted to the genset. So it's pulling the check valve open vs pushing it with flow.

This is a big CV too, with 3/4 NPT threads.

Questions are:

1. Should I try to find a check valve with a lower cracking pressure, or could mine actually be bad? Should 2 psi be easy to get it to open? I'm not sure how to test it properly. But me blowing through it is like I'm trying to blow up a balloon.
2. Is it ok to have this on the suction side of the pump, essentially keeping the whole fuel line and pump full of fuel? Will it work ok this way (Viking certainly thinks so, as this is how they built the boat).

Here's some pics of the check valve and fuel tank fittings. Thanks!

regulated air compressor is a good place to start....but you will need a sensitive gauge to do it accurately...

2PSI for cracking pressure seems pretty high to me...if circle valve will send you a 'softer' spring (lower cracking pressure) that would likely be the fastest path to closure. you would have to measure how much drop you have in that fuel line run to determine the appropriate cracking pressure.

the valve should be at the tank, to serve its intended purpose....an alternative would be an electrically operated valve...

and the pressure the fuel pump will deliver is determined by testing...more restriction in the suction side typically reduces the total volume delivered but depends on the pump details...the bigger concern with too large of a restriction on the suction side is today's fuel formulations vaporizing....

Thanks very much. You confirmed what I thought. This check valve was originally used with a mechanical fuel pump. I've learned they do a MUCH better job at pulling fuel (higher vacuum) vs electric which are better at pushing. So swapping to an elec fuel pump, but having a spring with this high of a cracking pressure is really the issue.

Well I went right to the manufacturer. He was actually surprised this "military grade/aerospace" check valve was used in a boat. The reputation of being overbuilt holds strong. Anyway, Circle Valve's customer service was excellent. After explaining the use, purpose and components of the system, the engineer recommended the spring just be left out. The pressure of the fuel trying to return to the tank due to gravity will be enough to seal the check valve and hold it closed when the fuel pump isn't running. But the cracking pressure to open the valve without a spring will be extremely low and should solve the issue with the pump being able to keep up. We will see! Easy test at least.

i would be very careful eliminating the spring...as doing so may eliminate the anti-syphon feature which would be my primary concern...and may be something that engineer may not know about....just my two cents...

Exactly right, but they are not required if the design of the fuel system is such that all fuel lines and fittings are above the tank. In those cases (as is mine), then the AS valve isn't required, as the boat does NOT have the means of siphoning fuel from the tank. It's an anti siphoning requirement, not a valve requirement. 33 CFR section 183.568 speaks to anti siphon protection. For reference: https://www.govinfo.gov/content/pkg/CFR-2010-title33-vol2/pdf/CFR-2010-title33-vol2-sec183-564.pdf

But thank you for that, as a lot of people may not understand it (I do though). This valve is strictly there to keep the fuel in the lines. I do still like the idea of a very light spring however, just to help the valve seat properly.

makomark said:

i would be very careful eliminating the spring...as doing so may eliminate the anti-syphon feature which would be my primary concern...and may be something that engineer may not know about....just my two cents...

Click to expand...

Just to follow up, as I thought more about it, I agree on the spring and decided it was too weak of a seal without it. But the one there was too tight. I went to a local supplier for an equal quality spring with less tension, but still accounted for tank head pressure, but was more in line with an anti siphon valve. It opens much easier (about 1psi required), but seals shut without a pressure on it.