I would think its more personal preference than anything. It works either way. The isolator is just to keep dangerous fuels out of the cab... I'm sure you know that. Now the "needle" valve, are you talking about the schrader valve in the test port? You'll need to remove that so fuel can flow to gauge.

It just came to mind that you might be talking about the "pressure snubber". The VP will send pressure spikes/pulses back through the fuel lines up 150psi or so. You cant see then on a regular pressure gauge but these spikes will KILL your pressure gauge..... I know I went through 2 of them. I got the Autometer pressure snuber fitting that just goes inline. Some people get a needle valve and open it just enough to get the full pressure reading and hopefully block enough of the pressure spikes to save their gauge.

Hope that helps.

 

It just came to mind that you might be talking about the "pressure snubber". The VP will send pressure spikes/pulses back through the fuel lines up 150psi or so. You cant see then on a regular pressure gauge but these spikes will KILL your pressure gauge.....

Hope that helps.

what you describe sounds like the reason isolators possibly fail. there are a few threads on the forum about isolator failing and leaking fuel.

 

when i got my autometer snubber it was too late.

my mech fuel pres gauge is destroyed now. dont even move.

 

When I did my fuel gauge install I "tried" to get the isolater to work... .. There is a bleed screw where you bleed off air in the line... stripped that crap out and it leaked like a siff.... So I tossed it in the woods.... Straight lined to gauge.. sealed up great at the engine... drops a little drop or two inside the cab even after 3 attempts to correct....

Before I did my install I spoke with an old mechanic I know and asked him what the deal was... of course he said keep fuel out of the cab... he is a old school drag racer so he said what they do is use an isolater... fuel on one side... gauge side fill line with Ethylene Glycol (Antifreeze)... He says that air will "compress" and you not get a accurate reading.... I didn't pressure him enough to figer out how to bleed the Ethylene Glycol out enough to get air out of the gauge side.?.?.?. worth a try.?.?.?.

 

I ran a hose to the electronic sender and then the wire to the gauge. With an electrionic gauge you don't have to worry about fuel or gylchol in the cab. Just make sure the sender is grounded.

 

I had two isolators fail both at very inconvenient times. I haven't used one since. A fuel pressure gauge setup should let you know you have a problem not be the cause of the problem.

I think a better question is "why use an isolator with diesel?". The tubing and compression fittings are rated for up to 200 psi while our trucks fuel systems are only going to put out about 20 psi. Unless someone purposely cuts the tubing it's unlikely you will ever have a leak. I used a grommet where the tubing comes through the fire wall and wrapped the tubing with wire loom for added protection. Even if you did by some fluke get a leak, it would be more of a fast drip than a stream of diesel because the needle valve restricts the flow of fuel. You would quickly smell it and shut off your engine. The needle valve can then be closed all the way so you can keep going.

I would run an isolator with a gasoline engine for safety reasons. Gasoline has a flash point (lowest temperature at which it can form an ignitable mixture in air) of -40 degrees Fahrenheit while diesel has a flash point of 143 degrees. Gasoline could possibly ignite and burn.

 

i run it without an isolator. never had a problem

 

Not all isolators are created equal!

The pancake style is very prone to failure. But the reason to ruin one is as much to save a gauge as it is to protect the motoring public and in many cases is required. Read, liability issues.

Running fuel or oil into the cab is never a good idea. Apart from potential fire issues (unlikely) the mess it can create can be a real bad thing. Also, the isolator does act as a snubber. The failure rate of gauges running no isolator is far higher than with.

If you are going to run fuel or oil directly into the cab, you should be using the correct materials and not 1/8" nylon. Get some pressure rated stainless -3 with full swivel ends that has been pressure tested. This only leaves a gauge failure to introduce fuel into the cabin. Seen it twice last week BTW.

Dave

 

been runing it with out a snuber for about a year now and not even 1 problem some fuel safe teflon on the threads and be done with it if you cant see a leak or smell it them your good am i right if the vp sent psi of 150 then you have a bigger problem than a blow gauge

 

So far I've been plumbed direct ot the gauge with a needle valve now for over 5 years and zero problems... The needle valve is set at nearly closed so the fuel pressure gauge needle rises slowly like a stock gauge so I know the fuel flow in the cab would be like drip if anything... As ofr a problem if there was you can shut the valve and problem dealt with...

As for me... I don't see any problem with being directly plumbed to the gauge. If you take your time to protect the line and insure it not going to get damaged on sharp edges of metal or pinched it will last forever...