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Old 18-05-2020, 15:13   #1
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purpose of check valve at outlet of diesel tank

I recently had a clogged check valve at the outlet of one of my diesel tanks. I hit rough weather and sediments got stirred up and some gummy debris got clogged up pretty good. I.e I could not even blow it back into the tank. I ended up pulling the tube to clean it. I also ended up opening the tank inspection port and cleaning it from the inside. To my surprise, It was not that dirty but in sloshing around all it takes is one gummy ball to get in there.

One of my fuel tanks has the check valve and the other doesn't. I got rid of it while under way so that I don't run into the same predicament. My primary, Racor 900 turbine series is better equipped to deal with this type of debris and not stall the engine.



Before i decide to permanently remove that check valve could anyone explain the purpose of it?
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Old 18-05-2020, 15:33   #2
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Re: purpose of check valve at outlet of diesel tank

It’s typical function is to serve as a useless failure point. Trash it.
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Old 18-05-2020, 17:42   #3
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Re: purpose of check valve at outlet of diesel tank

Only valve Iíve seen at the outlet on marine tanks is a anti-siphon valve. It stop any leak in the system from siphoning fuel out of the tank and into the bilge.
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Old 18-05-2020, 18:05   #4
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Re: purpose of check valve at outlet of diesel tank

What is a check valve? Is it a ball or gate valve to halt diesel flow to the engine?

You need to be able to isolate the diesel flow for a number of reasons including fire and filter maintenance.
A good tank design has the fuel take off above the bottom and a valve to drain sediments and water at the bottom of your tank. My system has both and the supply line ball valve is closed remotely by a wire in case of fire.
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Old 18-05-2020, 18:12   #5
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Re: purpose of check valve at outlet of diesel tank

Anti-siphon valves are USCG/ ABYC required in the outlet of permanently installed gasoline tanks, but are not required on diesel tanks. But they are frequently found in the hose barb fittings installed as a matter of course by tank builders and never given a second thought.

Over the years when I worked with boat builders on prototype diesel installations it was standard procedure to unscrew the hose barb fitting from the tank, take a punch or #2 Phillips screwdriver and knock the check ball and spring out of the fitting, and reinstall the fitting back in the tank/ suction tube.

As SV Illusion says, itís a useless failure point. Get rid of it.
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Old 18-05-2020, 19:26   #6
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Re: purpose of check valve at outlet of diesel tank

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What is a check valve? Is it a ball or gate valve to halt diesel flow to the engine?
.....
No, a check valve is simply a device to a limit the flow to one direction only. It will allow flow in the forward direction but prevent it flowing in the backward direction. Similar to a diode in an electrical circuit if that helps.
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Old 18-05-2020, 19:43   #7
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Re: purpose of check valve at outlet of diesel tank

Thanks for the clarification. Here in Aus we call them non return valves. Yes I can't imagine their usefulness on the supply line.
Hope you find any of the other info I supplied is useful.
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Old 18-05-2020, 20:33   #8
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Re: purpose of check valve at outlet of diesel tank

You need that check valve in some installations to keep the fuel system bleed. If fuel returns to the tank from the line, the line will have air in it. Upon restarting, the engine will run for a short while until the slug of air in the line reaches the HP pump. It will then stall. If a lift pump is installed below the bottom of the tank it's usually not needed. You are better off mounting the lift pump below the bottom of the tank than having a check valve IMHO.
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Old 19-05-2020, 04:49   #9
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Re: purpose of check valve at outlet of diesel tank

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You need that check valve in some installations to keep the fuel system bleed. If fuel returns to the tank from the line, the line will have air in it. Upon restarting, the engine will run for a short while until the slug of air in the line reaches the HP pump. It will then stall. If a lift pump is installed below the bottom of the tank it's usually not needed. You are better off mounting the lift pump below the bottom of the tank than having a check valve IMHO.
That's the best explanation I see. Thank you so much. Yes lift pump is below. That thing is not going back in.

I bought that tank new, custom made by a marine tank fabricator and they put it in, probably for those that have tanks below lift pump level.
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Old 19-05-2020, 13:48   #10
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Re: purpose of check valve at outlet of diesel tank

I'm with Illusion. I found one downwind of my raycor on my Perkins. Same problem. I used the same remedy.
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Old 19-05-2020, 15:30   #11
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Re: purpose of check valve at outlet of diesel tank

Installed by someone who did not know that they did not know. Remove it!
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Old 19-05-2020, 15:48   #12
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Re: purpose of check valve at outlet of diesel tank

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Originally Posted by DougR View Post
Anti-siphon valves are USCG/ ABYC required in the outlet of permanently installed gasoline tanks, but are not required on diesel tanks. But they are frequently found in the hose barb fittings installed as a matter of course by tank builders and never given a second thought.

Over the years when I worked with boat builders on prototype diesel installations it was standard procedure to unscrew the hose barb fitting from the tank, take a punch or #2 Phillips screwdriver and knock the check ball and spring out of the fitting, and reinstall the fitting back in the tank/ suction tube.

As SV Illusion says, it’s a useless failure point. Get rid of it.
Yeah, they are put on gas fuel power boats and only required for inboard engines IIRC. We used to put them in outboard boats but they caused some issues.
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Old 19-05-2020, 18:38   #13
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Re: purpose of check valve at outlet of diesel tank

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Thanks for the clarification. Here in Aus we call them non return valves. Yes I can't imagine their usefulness on the supply line.
Hope you find any of the other info I supplied is useful.
A check valve is usually at the tank outlet fitting and it is used to prevent fuel or gas from leaking or siphoning into the bilges if a line was to be severed or leaking in any way. How it works is when there is a vacuum in the line caused by the primary pump the ball moves away from the seat and allows fuel to flow. When the engine stops and the pump does not draw any fuel the spring pushed the ball against the seat and stops fuel flow. If the line was cut or leaking the pump could not create enough vacuum in the line to pull the ball away from the seat to permit fuel flow... it is a safety device.
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Old 19-05-2020, 19:01   #14
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Re: purpose of check valve at outlet of diesel tank

There is a difference between a check valve and an anti siphon valve.
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Old 19-05-2020, 19:12   #15
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Re: purpose of check valve at outlet of diesel tank

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Originally Posted by kmacdonald View Post
There is a difference between a check valve and an anti siphon valve.
there is hey...
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