Pressure testing a fuel tank / system

[mitiempo]

It would be pretty tough to pressure test a tank in a boat as among other issues you don't have easy access to all sides to check for leaks when doing so. My custom stainless tank was tested with 5 psi on the bench when made and checked with both soap and an ultrasonic tester which takes any small leak and amplifies it to headphones. A leak you can't hear with the naked ear becomes real obvious this way. By the way my tank does have a drain valve built-in with both a ball valve and a plug in the end for the future draining of it if ever necessary. I watched it being made and tested as the welder is a friend.
Brian

[RichH]

Originally Posted by Gladrags1

I think I may have a small fuel leak. When manually pumping the bilge, I get a bit of a sheen of diesel fuel. Granted that it could be from a previous owner's spill as a tablespoon of diesel will create a large rainbow but I would like to make sure that my aluminum tank that sits in the bilge is not leaking. I understand that a method of testing for leaks is to pump 3 psi into the tank and let sit for about 4 hours to see if there is any loss of pressure. I would like some advice upon the best tools to buy for this job. Or should I turn this job over to my diesel mechanic? Which will cost more - the tool or the mechanic? I have a shop air compressor. What else is needed?

Tod

Tod - what are the dimensions of your tank?
What are the materials of the tank?

Pressure hold testing: A few psi hand pumped into an empty tank, monitored by a large scale semi-accurate gauge, etc. should be fine to ascertain a leak-down or 'pressure hold' test for pin holes, etc. You will of course need to totally block (cap) the fill port and vent and check all the 'capped nozzles' with soapy water. Such pressure hold testing is NOT the realm of diesel mechanics .... and will cost you diesel mechanic prices for something that they do not ordinarily do ... .

Most metal boat tanks will develop pin hole leaks in the bottom (sump) along welds and sharp bends of the sheet metal. These areas are usually impossible to visualize - unless you have a 'bore-scope' that can fit through the limberholes under the tank.
An easier solution is to lay-down paper towels at the exit of the limberholes under the tank, and simply occasionally check for the paper to 'take-up'/absorb any emitting diesel oil .... much less hassle than doing a pressure hold test.

The good news for any metal tank is that you can (cut) open the tank, apply epoxy/cloth to suspect areas; then, 'reline' the tank with a 'lining' epoxy to seal any pin holes, etc. .... so you dont need to 'replace' a leaky metal tank. Lining epoxies are specially formulated to be rolled-on. A good source for small quantities of 'lining epoxies' is: Progressive Epoxy Polymers and Resins - Home Page Pittsfield, NH (a 'crappy' website but good products, including epoxies for lining potable water tanks, etc.)

[mitiempo]

Or you can replace the 22 year old tank and not worry about it for a couple of decades.
Brian

[Gladrags1]

My tank is shaped like an "L" that has been rotated 90 degrees clockwise. It is made out of aluminum, maybe cast aluminum??? It has 4 pickup tubes (1 fill; 1 vent; 1 engine pickup; 1 engine return; and 1 pickup for small aux diesel tank for diesel heater). All of the pickup tubes are on top and are either screwed into fittings or on a tube that is welded onto the tank. It holds about 45 gallons. It is installed so I can see the forward part of the tank down to the bilge but the aft portion (back 2/3) is hidden under the engine pan. I believe it would be possible to remove BUT I would have to remove the holding tank first and disturb the bilge pump, etc.

I REALLY like the idea of cutting off the top of the tank and lining it with an epoxy to avoid removing the tank. How does one reattach the top of the tank again? How long can the epoxy be expected to last? It is applied by roller? Downsides? Does it ever break down for possible clogging of filters?

Tod

[CrazyRu]

Ok. I have same problem. I have original tank installed in a bilge. There is not much access to aft end of the tank, and it is not easy to remove.
PO reported that he noticed oil/fuel in a bilge and installed new tank in cockpit locker, successfully blocking access to water heater, water pump and water tank and throwing boat out of balance - now I have water tank and fuel tank sitting on same side.

I removed fuel gauge/access plate from old tank and cleaned it and made storage for spare hoses and belts inside. Due to sinking (almost) accident (it is another story, everybody alive, boat is still floating) I filled the old tank with water. I didn't have time to remove water immediately and I noticed that water just staying in the tank, so there is no visible water leakage from the tank.
At same time I found leaking fuel filter housing at the engine. So I started wander if the filter was the source of a leak, and old tank is OK?

I need to do a lot of preparation to pressure test the old tank - blocking all inlets, installing plate back in a place, besides I don't have a gauge nor pump.

Can I just fill the tank with some sort of dye, some sort of water based paint and see if I get a color in a bilge?

It seems like it is most simple solution for testing old tank. If there is no dye in a bilge then tank is not leaking, right?
Do I miss something?
What dye to use?

[RichH]

[QUOTE=
I REALLY like the idea of cutting off the top of the tank and lining it with an epoxy to avoid removing the tank. How does one reattach the top of the tank again? How long can the epoxy be expected to last? It is applied by roller? Downsides? Does it ever break down for possible clogging of filters?

Tod[/QUOTE]

Drain the tank, fill with water, cut access holes (with sawzall, etc.) slightly smaller than final access hole(s), clean and epoxy-line tank, go to metal supplier or fabricator and have new access plates made slightly larger than what was cut from tank, ...... measure and locate 'stud hole' in new access cover drill evenly spaced (5/16") holes around the margin of the new cover AND into adhesive backed BUNA strip rubber gasketing. Overlay prepared new cover over access hole cut into tank then using 5/16" drill locate/mark the center of each hole .... then remove the plate and use a drill that is proper size for 1/4"-20 thd tap (sorry, Im traveling and dont have my drilll schedule for a 1/4"-20 tap - buy the tap and drill as a 'set'). drill the old tank access plate margins, then tap the holes and install 1/4"=20 bolts .... so that the bolt head (and star-lock washer) is inside the old tank and the threads are pointing up. Epoxy the bolt heads to seal them to the underside of the top of the tank. Install the new cover over the perfectly aligned holes using a THIN application of silicone RTV gasket cement on the gasket.

You will spend a little time and spend about 1/10th or less of what a new tank costs.

The hardest part of the whole job will be preparing and cleaning the inside of tank for the epoxy - use an aggressive 'garage floor cleaner' to cut the 'crud', etc. and get a small angle grinder (with 60-80 grit sanding discs) to roughen the inside surface after removing the 'gunk'.

[mitiempo]

Doing what rich says will work, but it'll be hell to do unless you take the tank out first probably.
Brian