Custom Fuel Tank Design Guide

7/30/2019 Custom Fuel Tank Design Guide

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CUSTOM FUEL TANK DESIGN GUIDE

This sheet has been designed to help you decide which type of fittings and accessories you require on your custom built dieselfuel tank. There are five points you need to consider.

Hose and Pipe Fitting connections

Avoiding Internal Baffles

Inspection Hatches

Senders

The Tank Drawing

These sections are described in detail in the following pages. Check off each heading as you cover them. You may decide thata sender is not necessary as you will be able to see the contents through the tank wall, so just ignore that section.

Hose and Pipe Fitting connections

First decide where the fittings need to go. Once you have established the position, the size has to be decided. Once the sizehas been decided, you need to check on the chart for the overall height or length of the fitting. This height or length can then bechecked against the tank design to see if there are any problems with clearance. For example, you may have a clearance above

your tank design of 50mm and want to fit an 1 elbow inlet. This would not be possible as an 1 elbow actually stands up75mm and would foul whatever is above the tank. The tank height would then have to be reduced by 25mm to allow for thefitting.

Please note that all straight hosetail fittings are screwed into a female BSP boss, which is permanently welded to the tank. Allfemale bosses will stand 10mm off the tank face when the fitting is removed. Female bosses are available in the followingthread sizes:

BSP BSP1 BSP1 BSP1 BSP

Smaller sizes are available and are achieved by using a reducing bush screwed into the BSP boss. i.e. a BSP is attainedusing a BSP reducing bush.

Straight Hosetails for connecting flexible hose.

Straight hosetails are required when connecting to a flexible hose. Size of tail should be the same as the bore of the hose youare using. These are normally the inlet/filler hose and vent hose. Feeds and returns can be flexible but a banjo type fitting isnormally used and is described later in a separate sectionAll straight hosetail fittings are supplied with a bonded seal also known as a Dowty Washer. These seals comprise of a zincplated steel ring with a stiff rubber seal bonded to the inside of the ring. The rubber seal is slightly thicker than the steel ring sowhen the hosetail fitting is tightened up the rubber compresses and seals the underside of the hosetail flange and the face ofthe female boss. The bonded seal does a similar job to a fibre washer but is far more effective as they are normally found inhigh pressure hydraulic applications. Hosetail fittings for fuel tanks are supplied in a marine grade brass and are available in thefollowing sizes:

Straight Hosetail sizes

Imperial Length (L) Metric Length (L)

45 6mm 45

5/16 45 8mm 45

52 10mm 52

45 13mm 45 53 16mm 53

56 19mm 56

1 60 25mm 60

1 63 32mm 63

1 72 38mm 722 72 50mm 72

L

Top of Tank

Dowty Seal

BSP Female Boss10

Brass Hosetail

Typical cross section of an assembled fuel tank brass hosetail.


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Jubilee Clips

Flexible Hose

Fixed Elbow Hosetails for connecting flexible hose.

Elbow hosetails are also used for connecting flexible hose to the tank. These come off a face of the tank and turn through 90.Tek-Tanks fuel tank elbows are of a fixed type and cannot be rotated once attached to the tank. See the drawing below.

It is important that the direction of the elbow is checked thoroughly

because if the direction is not correct the tank will have to bereturned to Tek-Tanks for repositioning. Elbows are available in thefollowing sizes:

Imperial Metric

6mm

5/16 8mm 10mm

13mm

16mm 19mm

1 32mm

1 38mm

2 50mm

Banjo type fittings for fuel feed and returns.

The banjo fitting used for fuel feeds and returns is a high quality fitting that can accommodate either copper pipe or flexiblehose. As standard they will accept copper pipe but with the addition of a special hosetail they can be set up to accept flexiblehoses. The beauty of a banjo type connector is that they can be rotated to any desired position. This can be a great help duringthe planning stage as the final directions do not have to be decided until the installation is complete. It is however a good idea tohave some idea of the positions so a neat installation can be achieved.

Feeds should be placed on the top of the tank as with all the other fuel tank fittings if possible. Gravity feed is now really a thingof the past as most modern engines have very good lift pumps. If the tank is a replacement for a gravity fed engine then we will

Fuel hoses should be double clamped as shown with theclamps opposite each other.

Hosetail fittings can be unscrewed if installation is tight forspace. If hosetails are removed then when refitting, do notover tighten smaller threads as they are vulnerable to beingstripped. If in doubt, do not remove.

Large fixed elbow shown. This elbow is

used for 32, 38 and 50mm hosetails. Allother sizes use a smaller body standing45mm high.

Most common sizes for fillers are 38mmand 50mm. Most common sizes forbreathers/vents are 13mm and 19mm.


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put the feed at the bottom of the tank but it is not advisable from a leak potential point of view. A gravity feed could possiblydevelop a drip after many years of vibration from the engine whereas a top feed would just show signs of seeping and wouldprobably be easier to see. A total failure of a gravity feed (for example a split or worn flexible hose), would almost certainly fillthe bilges with diesel.

Dip pipes are manufactured from 10mm OD straight copper pipe. Thecopper pipe is soldered into a brass reducing bush, the banjo fitting isthen screwed into the reducing bush and is sealed with a copper or

nitrile washer. The whole assembly is then screwed into a BSP bosswelded to the tank top or inspection hatch and sealed with a BSPDowty washer. See drawing below of complete assembly showing tankboss, reducing bush, dip pipe and banjo fitting.

Photo shows the two different setups for banjo fittings.

Dip pipes are normally left slightly short of the bottom of the tank so as not to pick up any water that may have condensated outor picked up with bad fuel.Some engine manufacturers will actually specify dip pipes on the fuel returns as the more powerful modern engines actuallyreturn the fuel back to the tank at quite a rate. This high return rate can cause foaming if there is no dip pipe. Return dip pipesare quite rare and can normally be ignored.

Each fitting needs to be checked against the tank design and the boat structure to avoid any problems later when the tank isfitted. Time spent now checking the size and position of each fitting will pay off, as it is normally not possible to modify the tank.

Please see the back of this sheet to see a typical custom tank drawing and how the fittings should be marked up. You may wish

to provide the information in a different format, which is not a problem as long as all the information is clear.


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Avoiding Baffles

When designing your tank, it is important that the fittings avoid any bafflesthat we put in. A custom tank can have fittings in almost any position, theonly restriction being the baffles. Nearly all custom built tanks will havebaffles unless the tank is very small, then it will have none.

The baffle spacing is based upon the length of the tank. All Tek-Tanks

custom built tanks have equal baffle spacing where possible. The spacingis normally between 250 and 350mm depending on how the lengthdivides up. For example a tank 1200mm long will have 3 baffles with fourcompartments 300mm wide. A tank 675mm long will have 1 baffle withtwo compartments 337.5mm wide. If in doubt about the number of bafflesa tank will need, then please phone for advice.

The same will apply to inspection hatches. An inspection hatch cannotstraddle two compartments; it has to be in one or the other. Please seebelow for dimensions of the 3 different hatch types.

Inspection Hatches

At Tek-Tanks we use 2 different types of inspection hatches on fuel tanks.

Standard nuts and bolts type.

The 200 and 270mm Standard nuts and bolts hatches are manufactured from the same material as the tanks (HDPE) and comewith 18 x M8 studs fixed from inside the tank. The hatch seats on a 3mm thick nitrile gasket and is fixed with 18 x M8 nuts andwashers. The height of the Standard hatches is 25mm, but this height can be reduced where space is critical to 15mm. Thereduction in height is achieved by counter boring the holes where the nuts and washers go and using half height nuts. Fittingand removal requires a 13mm spanner of socket. Fittings can be placed on the Standard nuts and bolts hatches. See photobelow:

Halmatic Pacific 24 fuel tank showing a Standard 200 nutsand bolts hatch. Fittings are an 1 BSP female boss toaccept a Wema fuel sender, and 3 x BSP femalebosses with 3/8 BSP reducing bushes (1 plugged).The other fitting is a hosetail which is the vent.


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Wema type hatches

The Wema hatch is the smallest and is ideally suited for the smaller tank. It is fixed with a single central bolt that screws into aninner flange and seals with a large O ring between the top flange and the tank. The hatch is 150mm in diameter and whenremoved the access diameter is 112mm. Fitting and removal requires a spanner.

Senders

At Tek-Tanks we use Wema type senders and gauges for remote sensing on the fuel tanks. These are a European specificationas standard with an out put of 180 when full and 0 when empty. American specification is available to order with the outputreversed. The drawing for these is shown below. All fuel tank senders are manufactured by Wema and have a prefix S2. Theinternal length of the sender would normally be specified by Tek-Tanks to give the best range and still allowing a slight amountof reserve capacity when the gauge shows empty. We stock Wema senders in 50mm increments from 200mm to 600mm.(Length is shown on the drawing as L. Longer senders are available to order up to length of 2000mm. Senders can bemanufactured to your exact dimensions if required, please allow 10 days for delivery.

L

27

For more details on these units please visit the website or phone for more details. The S2 series fuel tank senders screw into awelded 1 BSP boss. The boss is not removable but the sender is.

Tank Drawing

It is important to provide us with as much information as possible when designing your tank. We will need the overalldimensions and a clear indication of where the fittings are going to go. If the positions of the fittings are critical then they willhave to be dimensioned from the edges of the tank. If they are not critical then we will put them as near as possible to the

position indicated.When positioning the hatch or hatches, just remember to bear in mind where the baffles will be, again give us a call if you areuncertain.On a very complicated tank with many angles, please indicate any square corners if any. This will help us greatly when wecome to draw up the tank on our computer aided design system.


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Another method of supplying us with the information we need, is to supply us with a template or mock up in either plywood orcardboard. By doing this you can satisfy yourself that the tank can be easily installed and that you can actually get it in or out ofthe boat or vehicle. The template can then be marked up with all the relevant fittings and hatches and either sent to us flatpacked or you can bring it along to the factory to discuss in detail. The kettle is always on so we can discuss your design over acup of tea or coffe!For quotation purposes a drawing will suffice.

The following drawing is how we would ideally like the information presented but we do realise that not everyone is adraughtsman and has access to drawing programs. A hand drawn sketch is fine as long as all the information is there.

Tank design using computer

1200 220

400

200

300

A A

B

C

D E

Fittings

A = 200 Standard HatchB = 38mm Straight HosetailC = 19mm Straight HosetailD = 8mm Banjo to suit copper + Dip PipeE = 8mm Banjo to suit copper pipe

Proposed Fuel Tank for quotation purposes only.Mr. J. BloggsTel: 01234 567899Mob: 07777 888888Fax: 01234 567900

Hand drawn tank design

Documents

Custom Fuel Tank Design Guide