The Classroom

Maintaining your Propane system.

By  Capt. Wayne Canning

                Most modern cruisers are equipped with propane as their primary cooking fuel.  Northern sailors often use it for heating as well. It is perhaps one of the best cooking and heating fuels as it is readily available, clean burning and relatively inexpensive. Ease of transportation and storage add to its appeal. Despite its convenience propane does carry some hazards and although not very common propane explosions or fires can be tragic and devastating.
                As a Marine surveyor I get the chance to inspect many propane systems during my travels. I am often struck by how little effort is put into maintaining these systems considering the danger should a fault develop. The problem is not lack of concern or effort on the part of the boat owner but rather lack of knowledge about how to maintain their systems and where to look for problems.  With this in mind, having an understanding of the systems and how to maintain them is important for any boat owner using propane.
                Understanding a bit about propane will help you understand why systems are designed the way they are and how to avoid problems. Propane is a hydrocarbon gas that becomes a liquid under pressure, when the pressure is released the liquid becomes a gas once again.  This makes the storage and transportation of propane relatively easy because in a liquid form it takes up less space. Propane is heavier than air and will settle into a bilge just like gasoline fumes do. If you have ever watched the vapors from dry ice flow over and down the sides of a container you have a pretty good idea how leaking propane will flow. Knowing this it is easy to understand the major problem with propane, any leak will run like water to the lowest point in your boat. This can create an explosive atmosphere within the enclosed hull. Because propane expands as it is released from pressure a small leak can fill a large area relatively quickly. Propane needs the proper air/propane mixture to be explosive. The greater the propane concentration the harder it can be for an explosion to occur. Because a small leak can provide just the right ratio of air to propane, small leaks can be very dangerous. With the right mixture even a small spark can set off a powerful explosive.

                Most systems are relatively simple in design consisting of the propane locker, propane tank or tanks, a gauge, a regulator, a solenoid valve and the supply line consisting of either special propane rated hose or copper tube.  Although simple in design it is important to understand how all these parts work to remain safe. Let’s look at each part individually and then look at how they all work together starting with the propane Locker.  
                A propane locker is designed to prevent any leaking propane from entering the boat interior. The USCG requires lockers to be vapor tight to the inside of the boat and have a top opening lid with a gasket and latch.  Lockers also need to have a vent at the bottom that will vent to the outside of the boat above the waterline and at least 20” away from any other opening into the boat. This vent line must be a downhill run with no loops or dips to trap water and it should be a minimum of ½” ID.  All hoses and wires that exit the locker need to be sealed vapor tight. The propane locker tends to be the weak point in any installation as they are often not properly designed or installed. Do not assume because the builder installed the lock it is correct. Many older boats were built before there were many requirements.  Modifications such as adding hoses or wires can make matter worse by adding unsealed holes. Surprisingly I have found many builders do not properly seal the top of the locker where the sides meet the deck. A good test is to remove the tanks and fittings and completely fill the locker with water. If any water leaks into the boat you need to find the source and seal it. Lockers mounted on the deck or rails need to meet the same requirements as well. Extra care needs to be made with these exterior lockers to be sure they will not drain into any openings such as the cockpit, bilge vents or opening ports.

                The first thing that goes into the lockers is the propane tanks or bottles. Tanks come in all shapes and sizes but the most common found on cruising boats are the 10 and 20 pound sizes and very often one or two of the small 1lb camp stove bottles for a grill. The weight is not how much the tank weighs but rather how much propane it will hold. The 20 lb tanks are the most common size and are used on almost all household outdoor grills you can get at in the US. Although the 20lb tanks are the most common they are often too big for many boats, in which case the smaller 10 lb tanks may used. Most tanks are made of steel or aluminum although recently approved by the DOT are fiberglass tanks. The fiberglass tanks are lighter, non-corroding and have an added advantage that they are translucent so that you can see the level of the liquid propane inside of them.  The disadvantage to the fiberglass tanks is that they are not the same standard sizes of the metal tanks and may not fit your locker. If you are considering switching to a fiberglass tank check the dimensions of your locker and the tank first.  Tanks should be inspected for corrosion on a regular basis, paying particular attention to the bottoms and the valves.  Tanks will have an inspection date stamped onto them. They need to have a hydrostatic test done every 12 years. All tanks smaller than 40 lb in the U.S. are now required to be equipped with an OPD (Overflow Protection Device) type valve. You can tell if your tank has an OPD valve if the knob to open the gas valve is triangular in shape. These valves prevent the overfilling of the tank with liquid propane. It is important leave some room in the tank for expansion should the temperature of the tank be increased. To aid in this the valves are also equipped with pressure relief devices to prevent the tank from being over pressurized and exploding if super heated in a fire. The OPD valves are also setup so that propane cannot be released unless a device such as a regulator is connected to the valve. This means if you open the valve on a cylinder with nothing connected to it you might think it is empty as nothing will come out. This confuses many users into thinking their tank is empty when there is still fuel inside. Some tanks are designed to be installed horizontally only. These tanks have special brackets on them and a special pressure relief valve that will vent only gas not liquid propane when on their side. It is important not to use a horizontal tank standing up and vice versa because liquid propane could get into you gas line. This would increase pressure in the line as the liquid expanded, creating a serious fire hazard.

                Connected to the tank is the regulator and pressure gauge. The gauge is on the high pressure or tanks side of the regulator and is used for leak detection. Contrary to what some people think the gauge will not indicate how much fuel you have left in the tank. The regulator reduces the high tank pressure of around 100 PSI to a lower .435 PSI working pressure for your appliances. There really is no marine specific regulator however any regulator used should be preset or non adjustable and be UL approved. Make sure it is set for the correct pressure for the appliances it will be feeding. Most regulators are connected directly to the tank however you can have the regulator mounted remote with a high pressure hose connecting the two.  Keep in mind though the regulator and fittings must remain in the propane locker. Most installations use a single tank regulator meaning it is only connected to one tank at a time.  Systems with two tanks may use a double tank regulator that will automatically switch tanks when one runs out. The drawback to the two tank regulator is you may not notice the first tank run out and not get it refilled before the second tank runs out as well.
                The next fitting inline is the shut off solenoid valve which should be connected directly to the regulator and be inside the propane locker as well. This is an electric valve that is remotely operated. The solenoid valve is normally closed meaning it will not open until power is supplied. This is your primary safety device and should be left in an off position unless you are using your stove or heater. The remote switch to operate the valve must be mounted adjacent to any cooking device. It should also be located so that you do not have to reach over any burners in order to operate it. It makes sense to locate it so that it is in the direction of an exit as well. Although not required there should be a red light located near the switch to indicate when the power is on and the valve open. It makes sense to locate the switch separate from other switches and indicator lights so that it can readily be sighted and turned off if needed. This also helps ensure the valve is not accidentally left in the open position when not using the appliance.

                Connected to the solenoid is the supply line to feed the appliances. If you have more than one appliance, say a stove and heater each unit should have its own supply line originating within the propane locker. The supply line can be either rubber hose with permanently attached end fittings or copper tubing with flare fittings. All ends whether hose or copper tube, are of the flare type using only brass fittings. The supply line must be a continuous run from the propane lock to the appliance. The only place a connection is allowed is when using copper tube a flexible hose needs to be used when connecting to a gimbaled stove.
                When inspecting your propane system for potential problems it is best to star at the locker. Make sure the drain hose id open and does not have any traps that will hold water. Check the locker itself for cracks or gaps in any caulking. Check the seals around the wires and hoses where they exit the locker, makes sure they are sealed tight. A little silicone around the penetrations will help ensure a vapor tight seal.  Also check the lips gasket and latch to ensure they are in good condition. Next check the tanks for rust or corrosion. Inspect the valves and fittings at the top of the tanks, do the handles turn freely and is the over pressures vent on the back of the valve clear of dirt? Check the regulator gauge and solenoid for corrosion and inspect the fittings and connections.  Inspect the wiring to the solenoid making sure any connections are properly done and in good condition.

                If everything looks good it is time to start following the hose or tubing through the boat. This can be hard but it is important to inspect it the whole run. Problem areas often develop in hard places to inspect such as where the line passes through bulkheads. With copper tube you want to look for corrosion and that telltale greenish flaking on the surface. Copper tubing can look great for most of its run but have one some area of corrosion that can result in a leak. With rubber hose you want to be looking for signs of dry rot, those small cracks that develop on the surface. Also look for brittleness in the hose. For either type of supply line make sure it is well supported its full run and that it is not pinched of chafing where it goes through any bulkheads or dividers. Also make sure it is run separate from ant wire runs. It always surprises me how often I see wires tied to the gas line in boats. It would seem obvious why you would not want to do this but time and again I see it. Once you have followed the line its full length check the fittings at the end. If you have a gimbaled stove make sure the hose will not rub on anything for the full swing range of the stove. As this area is subject to movement you want to inspect the hose carefully for signs of wear. Also check the tightness of the fittings here by using a wrench. Fittings can get loose over a period of time. If you are at all not sure about the condition of your gas line it is best to just replace it.

                Once this visual inspection is complete and any repairs are made it is time to test the system for leaks. This is typically referred to as a leak down test. With your appliance valves all closed and the solenoid valve off open the cylinder valve fully. Note the location of the needle on the pressure gauge. You may want to use a piece of tape to mark the high side of the needle. Now fully close the tank valve and wait. Three minutes is the minimum time to wait but five to ten minutes is better. The needle should not have moved at all. If it has dropped more than five pounds you need to check for leaks. If no leaks are noted repeat this test this time with the solenoid valve open or in the on position and the appliance valves closed.  Once again wait at least five to ten minutes and note any drop in pressure. If you note any loss of pressure in either of these testes you need to check for leaks.

                To check for leaks it is best to use a small spray bottle with soapy water in it. Before you start it is a good idea to turn off any electrical power and open the boat up for ventilation.  It should go without saying, but never use a flame to test for leaks. With the tank valve open, the solenoid valve open and the appliance valves closed, spray each fitting with soapy water. Start at the tank end and work your way through till you get to any appliance. Spray areas where the hose passes through bulkheads as well as all the fittings. Leave the soapy water on the fittings for at least five to ten minutes with the pressure on. Look for small foaming bubbles at the fittings. If you note any turn off the valve at the tank and bleed off line pressure by opening the valves at the appliance before starting repairs. Once you have repaired any leaking fittings run the test again. If you do not find any leaks it is possible that your appliance is leaking. If this is the case it may be best to have a service technician check it out.
                Maintaining a propane system is relatively easy and will provide you with piece of mind but it does need to be done on a regular basis. I recommend doing a complete system check every time you refill your bottles.  Also try to make it a habit to do a leak down test before using your stove or heater. Always turn off your propane at the tank when you leave your boat unattended or if you will not be using your stove for while. Used carefully propane is a great fuel to have onboard, just take the time to make sure it stays a safe fuel.

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  1. Good post and descriptive, but having photos and a diagram as you go along would have added to it.

  2. Robert Smith

    Great article. I’ve always wondered why the test time isn’t something longer like 24 hours.

    • It would not hurt but for leaks large enough make an explosive atmosphere less time is needed to spot the leak. Thanks for your comment and thoughts.

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