Truck Mounted Water Tank 9

[alexM71]

Our company equips trucks with required equipment and structure for different applications.

We have a truck mounted with a 10,000 lit (2700 US gal) Poly Propelene tank (External Dimension height: 1600mm X Width: 2500mm X Length: 2800mm). The tank is mounted on a frame under the tank using bolts which are tightened directly on to the Polypropylene tank. This frame is mounted to the chassis through rubber flexible joints. There are no other supports or fixtures holding the tank except the above.

Our Engineering department claims that there are no issues and the type of mounting is sufficient. Unfortunately there is no study or calculation supporting conditions like when the truck applies a sudden brake, takes a sharp curve or drives off-road. We did a validation by conducting a road test, however we (as quality control) are looking for some supporting calculations which can ensure safety of the mounting system in the above conditions. Would appreciate if someone can throw some light on this. Thanks

 

[micalbrch]

That reminds me a bit on calculations which are done by car manufacturers who calculate whether the seats stay where they are when there is a sudden brake. My doubt would be more the flexible joints between frame and truck chassis than the bolts which hold the tank.

 

[MintJulep]

You are right to be worried.

Tear out of bolts through the plastic.

Cold flow of the plastic over time causing the tank to become loose.

 

[alexM71]

Can someone suggest a way to calculate the force that the mounting bolts may be subject to, in the event that the truck be driven in circles at a particular velocity etc? Thanks for any help in advance!!

 

[desertfox]

Hi alexM71
Those fixing bolts could be subjected to various loads due:- accelerating, cornering, braking, swishing of fluid in the tank and we have very little information from your post.
I would suggest you ask engineering department why they consider there are no issue's, do the trucks only run very slowly or are they roadway trucks?
You could also ask if they have considered the loads imposed on the bolts due to the things I listed above.

desertfox

 

[hydtools]

Interesting reading from NZ:

http://www.nzta.govt.nz/resources/h...-guide/docs/heavy-vehicle-stability-guide.pdf

Ted

 

[alexM71]

Thanks for your time desertfox,

In fact I discussed with our Engineering dept but it looks like things are running on assumptions and they are looking to have a design validation done by conducting a road test to simulate actual use of the truck. But I'm not convinced and believe that even if everything goes fine in a road test, there is still a risk factor.

I can provide any required details if we can have some reliable results.

The truck will be used for fire fighting and hence it becomes more critical to make sure there is no risk the way the tank is mounted. Thanks

 

[desertfox]

I found this which might prove interesting

http://www.roscommonequipmentcenter.com/projects/rec66.pdf

 

[TheTick]

Who's going to perform the high-G turn validation after 5 years of weather, with the tank 3/4 full after sitting in the hot sun all day?

 

[desertfox]

Its been done before look at these references on this site:-

http://www.roscommonequipmentcenter.com/

 

[dhengr]

AlexM71:
We really need some cross sections through the tank and frame, lengthwise and across the truck/tank frame, and details of the connections currently contemplated; including dimensions, etc. We can’t see what you are imagining from here. I would think you would want some baffling in the tank to control sloshing, maybe some soft stiffeners as part of the tank internals, and I would want two structural rails inside the tank and in line with the side sills of the tank’s support frame. What I would want to do is pinch the plastic tank shell btwn. the inside rails and the support frame members at many smaller bolting points, so as to distribute this loading to the tank shell. Then the real structural connections to the truck frame are made at the bottom flange of the tank support frame. These are concentrated load which the plastic tank shell would never be able to withstand.

 

[ornerynorsk]

Here in my locale it is very common to see these poly tanks in use by the ag industry. They are almost always secured by steel banding around the tank which fastens them into a cradle support. There is no way I would trust a bolted foot mount or other such arrangement, especially for highway use.

My 2 cents.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[rmw]

On the one hand, I am in the engineering department of my company and everyone else knows better than we do - production, quality, sourcing, even the truck drivers. Boy, they could do some really good designs if we would just get out of the way.

On the other hand, we in engineering do make some real boners from time to time, so I've been around long enough to know to listen to dissenting voices. If I can't justify my designs, I know to go back to the drawing boards (euphamistically speaking, that is.)

Are your engineers real engineers, guys who went to school, paid their dues, etc. and got degrees, or are they guys who are promoted draftsmen, ex-salesmen etc.? That could make a big difference in what opinion I form of their design from your meager descriptions. If the former, then they should be able to make a reasonable defense of their design approach and show you the calculations that justify their design decisions. There may be mitigating factors involved that aren't appearant to you. On the other hand, if they aren't really qualified for their responsibilities, then you may have a disaster on your hands and you are right to raise the alarm.

I'd like to hear from them if there is some way for you to post their comments.

rmw

 

[MikeHalloran]

Can you reveal who designed and manufactured this tank?



Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

Designed the tank?

Or, "designed" the bolts holding the tank on tot he bottom of the truck frame with only bolts holding it up?

I'd expect failure of the bolts pulling through the plastic around the holes. Begin an inspection program and look for trouble before you get sued for a hazmat cargo drop onto the freeway at rush hour. You (as part of the QA dept) can doi that much immediately.

Not good publicity there.

 

[zekeman]

I would take as a first approximation the maximum force on the vehicle to be due instantaneous braking, leaving the maximum coefficient of friction ( I found = 1.0, dry asphalt against new tire)as the limiting force= 1.0 *W
So the lateral force would be in the vicinity of the loaded weight of the tank. This would also be the maximum centripetal force no matter what the speed/arc radius.

Putting a safety factor of 2, I would calculate the design force to be

2*W

which would suffice for normal driving.

Also, fatigue life would have to be added to the force equation of the structural components as well as the flexible mounts life over weather and time.

However,collision forces would no doubt dominate all forces and it would behoove the designer to guarantee the integrity of the support structure under those extreme conditions; this would require an additional structure( bands for example) to prevent the tank from separation after shear failure of the main support.

 

[alexM71]

Thanks a lot for all the responses and for your time..
Very much appreciate the links posted.. some of them really gave some good information. What I noticed is, the vehicles I saw in one of the link does have PP tanks but those are too small and doesnt seem to pose any risk of shearing.
To have a better idea of what I am tryin to convey, I have attached some drawings which shows the actual vehicle and how the tank is mounted on to the vehicle. Hope this will help to reach some kind of calculations to understand how reliable the vehicle is, as far as the tank mounting is concerned. Thanks once again!!

 

[MikeHalloran]

Looks like you just changed the material spec on a steel tank drawing.



Mike Halloran
Pembroke Pines, FL, USA

 

[alexM71]

Mike, I really don't know what made you say that and why do you think I would do such a thing when I am seriously looking for a solution.
This is the drawing I got from our Engineering dept. I don't know if it was copied from a different project with ss tank as we do both PP and steel tanks.

 

[jtseng123]

This is not a tough question. Look at how NASA design the shuttle, you will know why. It is the "g" force you have to establish, forward, backward ( brake, accelerate), and sideway (cornering), and up and down if the driver hit a bump or pothole. Once you establish the value of "g" at each direction, you will know the force and any combination of the forces since it can happen simultaneously. All the forces will be then transferred to the bolts, structures, bracing. Do not consider friction to counter the force in case you have loose bolt or bracing.. Then check fatigue on all parts due to how many times it will occur.
We ship pressure vessels by all means: truck, railroad, barge, ocean ship, and the "g" factors are well established in order to secure the vessels.