Fragile diesel heater supply tube

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Nick F

Sep 2, 2020
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1974 Grand Banks 42 Classic, Hull 433
The supply line from the dosing pump to my diesel heater (Espar) is about 10 feet long and is a tiny nylon tube (2mm ID, 3.5mm OD). This tube is pressurised with diesel during opertion and still under tank pressure when not operating.

Is anyone else concerned about having what appears to be a very fragile plastic tube under fuel pressure in the engine room?

Has anyone used a different tube? I get the impression that Espar wants a very small ID tube - perhaps to ensure that any air bubbles get swept through. The smallest fuel hose I can find is 3/16" ID (4.8mm).

I wondered about encasing the Espar tube inside a rubber hose for protection along most of the run.
I would question whether the small tube is ABYC or USCG approved. Double walling the tube might help a burst hose but then it will still run out somewhere. I know Parker makes small hoses with fittings for diesel fuel. That is what I have on my Diesel fireplace.
It’s a small diameter thick wall tube for more than one reason. Besides sweeping out any air bubbles, the tube resists swelling when the pump pulses, much like a hard brake line. that’s why the thick wall. A soft hose will only be trouble and doesn’t have any better heat or chafe resistance than the hose they provide. Just route it properly and you won’t have any issues.
As said above the nylon tubing is part of the system performance. I would look at the parts diagram to see of there is a solenoid valve at the burner end. If not then there is no pressure on the line when power to the pump is cut. Protecting the nylon line from chafing is easy.
The complaints about diesel heater supply tubes seem to be with some of the Chinese heaters. They often ship with a softer line (typically green) that kinks, swells, and ultimately leaks.

I was just doing some research on various plastics and their resistance to diesel and other oils. Turns out that some are affected but degrade and swell slowly enough that they can be used in some aplications. Swelling like 1.3% after 90 days exposure. So even when a chart says "yes," the fine print might make it a "no" for some uses. And since there are now 16 gazillion types of plastic, it is a bit of a gamble.
1/8" copper tubing has a 5/64" ID. Cover it with hose in wear places.
1/8" copper tubing has a 5/64" ID. Cover it with hose in wear places.
I 2nd that, copper tubing supported every 12 inches. Make sure your filter is easily accessible or it won't get changed
Cheers J.T.
I would stay with the original tubing, but put it inside another tube for safety. Think of it as running a number of wires, but inside PVC conduit. 1/2" PVC or 1/2" PEX would certainly protect it.

The only problem with copper tubing is that it transmits, and seems to amplify, the "tick" of the pump. I have my pump loosely strung on a zip tie instead of screwed to the bulkhead (it came with a rubber mounting clamp that would help some in reducing the tick transmission.) The pump is also covered with a piece of "smurf tube" type of pipe insulation. It has copper tubing up to about the last 4 inches, which is then rubber fuel line to reduce the tick transmission into the copper.

The reason for going to this extreme is that my pump is in the engine room directly under the dinette seat that converts to a double bed. With all of the sound attenuation, it is fine to read on the dinette bed in the evening without hearing the ticking. We seldom sleep with the heater on.
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