Technical Design of an OIL CATCH TANK

As highlighted in our previous blog, the need for an Oil Catch Tank. Not just any old oil catch tank, a properly designed tank will be much more effective at separating oil mist and vapours. In the past I have seen Oil Catch Tanks made from Tin Cans, Drinks Bottles, Plastic food containers and all sorts, by far the best option in effectively separating oil and vapours. Lets have a look then at manufacturing an effective Oil Catch Tank. Below we can see one of our “technical” (lol)

beginnings of a catch tank design.

From our sketch we need first to produce a sheet metal cylinder. A couple questions pop up here immediately. We know size of cylinder we require (e.g. the diameter of the can 100mm) but we need to mark this out from a flat sheet of material (in this case 1mm mild steel). Hence we need to know the circumference around the cylinder to know how long the panel will be in the flat sheet state before rolling. We work this out using a simple formula – ∏ (symbol represents “pie”- 3.142) x diameter = 3.142 x 100 = 314.2mm (which is the flat length of sheet required before rolling up. So we will need a flat panel of sheet cut out 314.2mm x 140mm long (height). We can now go ahead and mark this out to size with a rule and scribe, cut out using a guillotine (or tin snips, or grinder and cutting disc) and de-bur (remove rags on edges) caused by guillotining / cutting – remember safety 1st – use goggles / gloves / personal protective gear!  The next stage is to set up our rolls to roll a cylinder- in this case we have “Pinch Rolls”, which are particularly for sheet metal (up to 3mm thick). You may notice from the image above that Pinch Rolls are set up with 2 rolls above and below each other. These rolls grip the sheet material between them and drive it forward and back, the 3rd roll at the rear is adjustable up and down, this can then be used in turn to add pressure to the material being rolled through the top and bottom rolls and produces the pressure to lift the material and “roll” it into a cylinder. Obviously the more pressure added from the rear roller the “tighter” the cylinder diameter will roll up. A technical point to note then before rolling thin sheet is to “Break the Grain“, this is a process where the sheet is rolled one way then another, turn it over and repeat, offer sheet into the rolls at an angle and roll one way and then the other. This is only ever done to put a very shallow curve into the panel to remove any “memory” the sheet may have. This occurs when a sheet has been taken from the inner of the “coil” of sheet material as it is transported from the mill to be rolled flat and cut into manageable size sheets.

Most sheet comes in sizes of – 2m x 1m 2.5m x 1.25m 3m x 1.5m 4m x 2m, So before we roll our panel into a cylinder to form the main body of the catch tank we also need to check that the sheet panel is square, otherwise once rolled up into a cylinder one edge may be longer than the other. An easy way to do this is to check the corners with an engineers square. For larger panels it is just as easy to measure diagonally across each corner – corner, if the measurement is the same then the panel is “square” if not then it proves that the panel can in effect be a parallelogram; which we don`t want. Once “rolled” to the correct diameter we can clamp, tack and weld the joint which runs longitudinally along the cylinder – I use a “TIG” welder to produce a nice even – more importantly “leak free” welded joint.

See below Image of all parts to make the catch tank

So you can see the rolled shell, the domed bottom, flat top, angled baffle, perforated baffle plate and barrel fittings which will be cut in half.

Once all parts a made, the “tack” up stage can begin; tack up is important as all joints need to be a close fit joint due to the fact that the material is only 1mm thick this can easily be “blown away” by welding once heat has been built up in the joint.

Image above to the left shows the a bad tack up of the base of the oil catch tank to the main body. As you can see I have allowed too much heat to dwell in one point and not added enough filler wire and hence a small hole has blown through the joint. This was easily remedied by a small pulse of heat and a quick filler material addition to fill the hole.

The image above to the right shows the main body with baffle plate tacked in place to the back of all 3 inlets (inlet holes shown). The idea of this is that the oil mist hits the vertical baffle plate and is aimed towards the bottom of the tank where the mist hits the perforated baffle plate where oil will settle and drain to the bottom of the tank to return to the sump. Vapour will then head up and out of the top mounted filter where any remnants of oil will be filtered out before it vents to atmosphere.

Once all the parts are fully TIG welded to the main body of the catch tank I need to pressure test the tank to ensure that there are no leaks. This involves “bunging” up all the inlets / outlets with caps or tape, leaving one free to connect a compressed air line to. This is then turned on to add pressure to the tank (usually no more than 1bar) is sufficient. Once ready there are 2 ways to test – either submerge the whole job under water and watch for small bubbles leaking out of any joints or – brush all joints with soapy water (I usually use fairly liquid mixed with water about 10 to 1 ratio) and again watch for bubbles that the leaking air will produce. Both methods need a constant pressure to be maintained in the tank whilst testing. Any small “pin hole” will quickly reveal its self by a steady stream of bubbles appearing from the point.

I always test tanks of any description initially with about 1 bar of pressure, if they have brackets I will test the tank before welding on brackets and then up the pressure slightly and test again after welding any support brackets in place.

This ensures double checks are made and tanks are delivered to customers 100% leak free – in 10 years I have only ever had 1 petrol tank leak – one that happened to go to one of my longest standing customers, needless to say it was on his own personal race car and I felt like such a fool. None the less I repaired it by washing the tank out with a pressure washer and then filling it with inert gas (argon) to reduce any chance of explosion by any fumes that may still have been present in the tank. Job done. This is not recommended to be undertaken by anyone other than a “professional” as the tank could explode in your face while welding and cause burns and severely nasty injuries.

Once the tank was complete a bit of a clean up with an abrasive pad and a thin coat of oil was added with a rag to stop the tank rusting. This was because the customer decided he wanted to paint the tank to match his car.

Completed tank before painting –

I hope this Blog has been of some intuitive help to someone. If you have enjoyed this Blog please remember to sign up to receive updates every time a new article is added – see the left hand border for sign up information.

Thanks for reading 🙂

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