Auxiliary Tanks 1

In this topic we will look at the range of storage tanks, their pro's and con's, and how to decide on which tank to choose and install correctly.

Stainless Steel

Stainless tanks are the best option of all, they can accommodate all the liquids used on conversions, water, fuel, grey water, etc; and all without problems of contamination or leakage. Stainless steel does have one flaw, this is its ability to crack or fracture under flexing, and as we all know all true 4X4's flex considerably, so its issue is that of mounting it correctly. Stainless has another flaw, this is its problems with electrolytic reaction, this is where it comes into contact with another dissimilar metal such as steel, if this has any amount of electricity flowing between the dissimilar metals the less noble metal, mild steel in this case, corrodes excesively rapidly, and as all vehicles use the vehicle body as earth we have this condition.

Mounting stainless tanks correctly is not difficult, we have to allow it flexibility so it can move and isolate it electrically to prevent electrolytic reaction from occuring. If we look at a chassis mounted stainless tank we make the mounting brackets from mild steel which is the same material as the chassis, we then insert mounting rubbers, the bobbin types are best, and bolt them to the chassis brackets we have made, the tank then sits on top of them so the weight is pushing down onto the rubber bobbins, this is important. If we use mounting bobbins the other way round and suspend or hang the tank from them we can encounter problems if a rubber bobbin is damaged one corner of the tank is not suspended and can cause cracking.
Installing a rubber bobbin is simple, but we have to consider the stud or threaded portion is made from mild steel, and we do not want this in contact with stainless, to isolate them we use a plastic isolation washer, this is merely a plastic washer which has a stepped portion. The lower washer is fitted over the top threaded portion of the bobbin with its step facing upwards, the tank is dropped onto the washer so the stepped portion is inside the mounting hole of the stainless tank. The top washer is placed on top of the stainless tank mounting hole with its stepped portion facing downwards into the stainless tank mounting hole, a mild steel washer and nut is then fitted. We now have a flexibly mounted stainless steel tank which is electrically isolated to prevent electrolytic reaction.

All the above also apply to aluminium tanks, although they have less propensity to cracking than stainless steel they are aluminium, and a dissimilar metal to mild steel and will create electrolytic reaction.

Plastic Tanks

Plastic tanks come in a range of types, they have to be of the right material to suit individual applications, for water tanks they have to be made of a food grade material, and fuel tanks have to be of a suitable material for fuel, the two cannot be interchanged. Plastic tanks can encounter problems with fuel, particularly with petrol as they, being plastic, break down over time and becomes brittle, this leads to the tank becoming porous and leaking fuel, the recommendation is that fuel is not carried in plastic tanks permanently mounted on vehicles.
Plastic tanks are flexible and do not suffer from cracking, and can be bolted directly to any other material as they are not metal and do not suffer from electrolytic reaction.
Plastic tanks can suffer in cold weather, in freezing conditions their contents can freeze, particularly water, and any impact can fracture them.

GRP or fibreglass tanks should never be used for storage on any vehicle, GRP is porous by nature and its contents will enter the reinforcing matting and force the tanks to delaminate. Delamination is where water enters the matting and the continual heating and cooling makes the water expand and contract, this forces the polyester resins apart, much like driving a wedge into wood.
GRP releases a product called styrene into water, this is poisonous and can cause serious injuries, if it comes into contact with fuels it reacts with them and it breaks the polyester resins down into globules which blocks pipes.
GRP or fibreglass tanks should therefore not be used on vehicles.

Steel Tanks

Steel tanks can be used for fuel, but not water, they flex without cracking but have a propensity to rust and many see this as a problem. Steel tanks can actually be used for water if they are lined, they must be fully prepared and have all their fittings installed, a liquid food grade epoxy is available for lining them, this is a two part material which is mixed and poured into the tank, the tank is then swilled around so it covers every internal surface with the food grade epoxy. It is recommended this is done at least twice, and three times is better so every piece of the tanks internals are covered. Never epoxy line a mild steel tank then fit the fittings as there will be exposed steel surfaces which can and will rust.

Mounting Tanks

Tanks can be mounted anywhere on a vehicle, heavier tanks should be mounted as low as possible to prevent the vehicle from becoming top heavy, or raising its centre of gravity excessively, this is why chassis mounted or flat boot mounted tanks are the best for larger quantities of water. Footwell tanks, unserseat tanks, and even bulkhead mounting tanks are available, so there is a tank available for every space available on a vehicle.

Fuel tanks should never be mounted in front of the engine, the same applies to jerry cans, if a can or tank suffers an impact and leaks, the fuel will be driven straight into the engine by the forward motion of the vehicle and its cooling air, the safety implications are obvious to all.

When plumbing tanks into a vehicle we have to consider its application, only food grade pipe should be used for water tanks, this is not suitable for fuel, and only fuel pipe should be used for fuel, and not water. Pipework connecting tanks should always be of a suitable plastic, and incorporate a little slack to allow for any tank movement from flexing, this is particularly important on off road vehicles.
Always use stainless steel or plastic clips to connect hoses to tanks, and always use two clips at each termination if there is enough room, this gives a little more security. If copper or other pipe is used for a permanent tank installation then always ensure it is connected to a mild steel or stainless tank with a piece of the appropriate pipe to prevent electrolytic reaction from occuring.
Always clip pipes securely to the body or chassis using plastic clips of the right size, and always use more than necessary, always protect tanks by fitting underbody protection, particularly with plastic or stainless tanks.