[neil100]

I only ask the question because I have just Designed a Frame for a 400ltr Flat Baffled tank for my sons Fiat Doblo van.

I am not an enginer, But I have looked at how my tank as been fitted out in my van by Facelift, and tried to draw Parallels with it.

I showed the design to the Fabricators this morning, they said I have got most things right but will change just a couple of things on it.

I have asked them not to build it just yet because I went to see someone last night who I have known for 30 years. He teachs enginering at Blackpool college.

I sat there with my mouth wide open at His knoweledge. He as offered to design it for me, so it will be as strong as it can be from any collision, front, rear, or sideways.

He explained what would happen in a collision, Where the force is transmitted to if you have an accident, He said do you want me to work out much force would be appllied to certain bolts in the event of an accident if your tank was fully loaded.

I was amazed by his knoweldge, I showed him a photo of a wfp companys tank. He said it was alllright but their was so much more they could do to make it stronger and safer. He nearly fell to the floor when he saw how much it cost.

Why so Dear he asked?

He said I had made the right choice in tank, But it left me with a cold shudder as companys are selling wfp tanks, But how good are the people who design the frames for them?

Nel.

[jeff1]

Nel I'm still a trad, but in the new year changing over to wfp,
But I am going to use a trailer mount, and already have my breaked trailer.

I'm pretty good at welding and have my own mig welder, what type of cage would be the best for a trailer mount? Or anyone else with the answer please!

[JM123]

Nel I'm an qualified Engineer (Beng hons Chemical Eng) and (BEng hons Mechanical/Electrical/Electronic and Manufacturing)

Too many tanks are fitted without much consideration to safety - use your Engineering friend - he knows what he is talking about (assuming he is a lecturer then he most probably is qualified to Phd level)

To start with many of the steel cages I have examined for myself have OBVIOUS weak points, a good tank cage design is imperative to the safety of the driver/passengers etc - I have seen cages fitted with M8 steel bolts which although strong, would probably not absorb much of the kinetic energy released in an impact - the material of not only the cage - but more importantly the bolts holding it down is probably the single most important factor to consider.

Your friend will no doubt tell you of the importance of design not only for strength, but also for absorbtion of energy.  Think of crumple zones in cars, they are designed in such a way that they will deform, the result of this absorbtion of kinetic energy is sound and  heat (bend a spoon and feel the crease).  Personally I would ask him to design a chassis for the tank, then take it to the fabricators, making sure they have not only produced EXACTLY what is on the design drawing but also that they have used the same materials specified.

I'm sorry this is a little long winded but safety is paramount in my book.

[George P]

cost may have something to to with the blame factor as a poorly fitted / made tank may not withstand impact well as youve said and could cost dearly to either suppliers or there insurance. we had a 1000 ltr tank fitted by facelift and was nearly full to approx 950ltrs, after an impact of around 70 mph the tank moved slightly within its cage but the cage never moved - only damage to tank etc was a broken connector at bottom so all water poured out - police thought it may have been fuel but were glad it was only water. point being the differance of a poorly made or fitted tank could have had very differant results - it had not shot forward onto driver etc (although van did have bulk head fitted i dont know how good that would have been in this instance) also dont want to find out. out of interest van had front and side impacts.

[neil100]

Thanks for the replys.

Its nice to know you walked away George haveing an accident at that speed.

My 800ltr van tank was made and fitted by Facelift, so hereing your story makes me feel more confident that my tank will not come crashing through my bulkhead.

I now have his design and its very simple, It basicly is taking a sheet of stainless
steel and cutting out the corners. Then useing a special machine to fold it to the shape of the tank. Then stich welding the seams. Putting angle iron at the back and front and useing high tenstile steel bolts with big washers drilled through the angle Iron and van floor and plates underneath.

My freind says because it is sheet steel it will absorb a lot of the impact if involved in accident and put less strain on the bolts, He agrees with you JM123 that the bolts are what will bear the brunt of the impact.

He says it will cost more in raw materials but save in labour costs as their is a lot less welding to do. The Fabricators are giving me a price on both designs, so I am waiting till Tuesday and then decidieng with my son which will be the best option.

I know the fabricators are very good who are doing the work, They have allready changed some of my design to make it stronger and look better.

Many thanks. When its done in a few weeks I will post some pics.

Nel.   

[JM123]

yeah he's absolutely right, the secret is to be able to dissipate as much of the kinetic energy into the floor of the van and cage material as possible without the cage or tank breaking free - I am in the process of designing tank chassis for 400/650 and 900ltr tanks.

One of the things Nel's mate has included in his design is angle iron at the rear of the tank - this is something that is missing on many chassis designs, in an impact the tank will tend to flip up at the back, so the rear of the tank must be securely fastened - failure to do so may result in the tank lifting at the back, so you can imagine the tank will tend to pivot around the front of the tank - exerting torque on the assembly at the front, this torque results in shear forces and may cause the tank to break away - again this is a little long winded but its good to know your friend is designing a SAFE chassis.