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Fuel pressure gauges and needle valves

Mopar1973Man
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Mopar1973Man

Mopar1973Man

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Ok Gang...

I've seen a bunch of you wondering about needle valves... Well here I'm going to explain the reason and why needle valves should be used on all fuel pressure gauges including electric gauges.

Now first thing first is why do we need a needle valve? Well the needle valve is a adjustable damper for the fuel flow. It prevents harsh or water hammer pulses from reaching the gauge or sender.

What is water hammer?

http://en.wikipedia.org/wiki/Water_hammer

Here is what the pulse looks like...

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But now figure that is pulse open and close at half the RPM's but for 6 cylinder. This pulsation with eventually wear out or eat the gears out of mechanical gauge or electric senders.

So here is a quick video of proper set needle valve...

http-~~-//www.youtube.com/watch?v=M33ZCc8b-7Q

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  • 1 month later...
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Mopar1973Man

Mopar1973Man

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This is what happens to a electric gauge after water hammer has beat it to death... :rolleyes:

The wild swinging up and down is from the water hammer beating the rheostat back and forth till it wears out or damaged the sender so now you get this wild gauge problem... So you must protect both mechanical gauges as well as electric gauge just the same...
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jumpjg

jumpjg

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Good info Mike, New guy here, new owner, first post. Came across the thread while searching the forums for info on gauges. Questions:1) When you refer to a needle valve, is this like the needle valve used to tap into my water line in my house for the refrigerator's ice maker? Brass, tee handle, 1/8" NPT male to 1/4" compression fitting.2) Is this a better way to go than using a snubber that is offered by the gauge manufacturer?3) Is it OK to mount the sender directly to the engine, or should it be remotely mounted to the firewall/inner fender?4) Is it recommended to tap the fuel pressure at the fuel filter or would the input banjo at the injector pump be better?Appreciate the help,Joe in St Louis'99 3500 QCLB, DRW, 2WD, Auto, 4.10 Axle, Stock

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ISX

ISX

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Good info Mike, New guy here, new owner, first post. Came across the thread while searching the forums for info on gauges. Questions: 1) When you refer to a needle valve, is this like the needle valve used to tap into my water line in my house for the refrigerator's ice maker? Brass, tee handle, 1/8" NPT male to 1/4" compression fitting. 2) Is this a better way to go than using a snubber that is offered by the gauge manufacturer? 3) Is it OK to mount the sender directly to the engine, or should it be remotely mounted to the firewall/inner fender? 4) Is it recommended to tap the fuel pressure at the fuel filter or would the input banjo at the injector pump be better? Appreciate the help, Joe in St Louis '99 3500 QCLB, DRW, 2WD, Auto, 4.10 Axle, Stock

Yep, same as the one for the fridge. Probably better than a snubber. Firewall is better because of engine vibration. The banjo bolt and fuel filter should be the same pressure if it is the part of the fuel filter that is after filtration. Let me know if you ever need any help, I am in MO too..
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Mopar1973Man

Mopar1973Man

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Good info Mike,

New guy here, new owner, first post. Came across the thread while searching the forums for info on gauges.

Questions:

1) When you refer to a needle valve, is this like the needle valve used to tap into my water line in my house for the refrigerator's ice maker? Brass, tee handle, 1/8" NPT male to 1/4" compression fitting.

Needle valve I'm using is a NAPA (Weatherhead) #WH6820 it cost about $8 bucks...

Posted Image

2) Is this a better way to go than using a snubber that is offered by the gauge manufacturer?

I prefer the needle valve it because a snubber is just a fitting with a tiny drilled hole. But a needle valve you can adjust to taste. Also if there is a fuel issue you can just shut the needle valve and keep driving.

3) Is it OK to mount the sender directly to the engine, or should it be remotely mounted to the firewall/inner fender?

Lot of people suggest remote mounts... But is not really needed (In my opinion). Think the oil pressure sensor and all the other senders do well on the engine...

4) Is it recommended to tap the fuel pressure at the fuel filter or would the input banjo at the injector pump be better?

So I would hook in as far from the VP44 as possible to get back from the water hammer but you got to be forward of the filter so at the bottom of the filter is perfect. Because the stock fuel filter always has a head of air in the top of the filter housing and aid in some of the water hammer suppression. Not a good a idea to hook up at the VP44 because that is the source of the water hammer so the wave is the strongest here... (Most damaging effect!) Kind of like stand at ground zero and light a stick of dynamite BOOM! You'll most like be dead... But light a stick of dynamite and throw out a distance from you I'm sure you'll survive the BOOM! and might still feel it...

Posted Image

Appreciate the help,

Joe in St Louis

'99 3500 QCLB, DRW, 2WD, Auto, 4.10 Axle, Stock

My :2cents: in blue... :thumbup2:

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mopar440cu

mopar440cu

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My :2cents: in blue... :thumbup2:

Hey Michael, question where did you tie the needle valve in to the airdog system? I have an electrical Isspro fuel gauge and need to install a needle valve and stumbled on this old post. I appreciate the info.:thumb1:
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KYcummins5.9

KYcummins5.9

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Thanks... Is a 1/8" needle valve sufficient to feed to my isolator?...i went by napa and thats the only size that they could order...now its gonna be next week before i can get my guage installed i watched your needle valve setup video..are you using an isolator??? If so, where did you mount it? thanks in advance
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dripley

dripley

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He has no isolator. I set mine up almost identical to MM's. Needle valve in the line between the fuel filter canister and the vp. Piped straight to the mechanical gauge in the cab. Mike is my hero.post-10340-138698205348_thumb.jpgthere's you some love Mikey.

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dripley

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I have mine tapped into the #5 fuse in the fuse box in the cab. I have this little thingy that after removing the fuse you plug it into the fuse box and replace the fuse. I put it in so long ago I dont remember what you call it. It came with my gauges. The #5 fuse is the illumination circuit for the dash lights and will dim with the dimmer control.

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