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Vacuum Truck

07/06/2008 3:57 PM

I need to remove sand and water from a holding tank 25 ft below ground level, using a vacum truck.The vactruck has a 4"inlet. If I reduce the suction hose to a 2" from a 4"will the volume be reduced and the velocity increased thereby making it easier to lift the product from the tank Thanks

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#1

Re: Vacum truck

07/06/2008 4:35 PM

'If I reduce the suction hose to a 2" from a 4"will the volume be reduced and the velocity increased thereby making it easier to lift the product from the tank?'

Good question...
My answer is 'I don't think so'
I think it will either lift that head or it won't.
Changing the diameter won't change that, it will just change the flow rate of the material, and the smaller dameter may flow faster* but will add resistance to flow resulting in a lower volume per minute.

(* A faster velocity but at a smaller cross section will actually be less volume per minute)

Del
(I reserve the right to be wrong on this, but I'd bet a small sardine or two if pressed.)

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#2
In reply to #1

Re: Vacum truck

07/06/2008 5:13 PM

It takes approximately 0.4 PSI to raise Water 1 Ft. That will only raise it that far and if you want to move that water you need higher Vacuum (Negative Presusure) to accelerate and move it.

Most pumps are rated around 21 Ft. for pumping water using vacuum and that is at Sea Level on an average Barometric Pressure day of 29.92" of Mercury (14.5 PSI) As we know Barometric pressure changes with the passing of Atmospheric Pressure systems, High and Low Pressure systems, and not all Vacuum producicng systems can actually produce full vacuum only about 85% on normal Vacuum pumps.

Dividing 14.5/0.4= 36 Ft. but again that would not allow any energy for moving the water, only enough to get it to the top of a 36 Ft. pipe on an average pressure day at Sea Level.

You can pump water to dizzying heights but only about 21 Ft. with Vacuum at normal Atmospheric Pressure.

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#3
In reply to #2

Re: Vacum truck

07/06/2008 5:49 PM

Yeah..1 bar = about 33feet of water.

So 26 feet should be possible...but I don't know about the density of silt laden water.

However..I was answering the question as put. E.G The effect of hose size.

Del

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#4

Re: Vacum truck

07/07/2008 12:32 AM

I have read the post again and think that maybe in this case the OP is talking about using a vacuum pick-up rather than a suction pump.

If the air flow through the vacuum is fast enough to cause "blobs" or droplets to be separated from the sufrace of the tank sludge and those blobs are carried along in the air flow, then maybe it is possible to suck the water/sludge mixture from that depth. (Provided the air velocity maintains the liquid in droplet form as they move through the pipe. Probably call this phenomenon an "air venturi")

A bit like sucking rain filled air up through the pipe.

I am certain that a standard pump would not work, as 25ft below ground level plus another 3 or 4 ft to the bed of the truck where I imagine the pump to be mounted would cause the well know problems as described by others earlier in this post.

Reducing the pipe diameter for the same air flow would create faster air movement and thus greater potential to lift individual particles/blobs, but I don't know whether the net effect would be greater or lesser material recovered.

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#5

Re: Vacum truck

07/07/2008 1:46 AM

If you reduce the pick up line you will slow down the process most likely buut it would work if sand if all there is in there to pull out.

Your going to need a lot more water than what is in the tank to get all the sand out. I would estimate about 10 parts water for every 1 part sand pulled out. Just a rought estimate so be ready to add water if you really want it clean.

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#6

Re: Vacum truck

07/07/2008 2:08 AM

Del was correct when he said that the theoretical maximum by suction alone is about 32'. In practice the best we could achieve on a straight suction lift is about 28' (from the pump). You were also partly right when you suggested going for a smaller hose might help. The answer here is that you are no longer depending on vacuum to lift the sand and water out, but allowing the air velocity to become the transport medium. This will work down to about 45', provided that there is plenty of air being sucked through and that the hose is never allowed to block and the velocity is maintained. Yes, it will work but be prepared to spend a bit of time doing it.

Regards,

Pete.

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#7
In reply to #6

Re: Vacum truck

07/07/2008 2:38 AM

Pump will not work at this hight( 21feet) to lift water and sand .the water will get vaporise at this vaccum.

The best way is to lower the pump below and keep around 8/10 feet above and then use the vaccum.

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#8

Re: Vacuum Truck

07/07/2008 8:53 AM

The commercial "Sewer Suckers" use two types of blower. One is the positive displacement. They are very effective on wet material and need a seal at the end of the hose, which can be 8-10" dia. The other is centrifugal. It moves a lot of air at a relatively low pressure. Material, wet or dry, is entrained in the air flow. This will move anything that will fit into the hose (10-12" dia). I've seen bricks picked up by both of these systems. With the lift you need, you probably should use the air entrainment system. Vac-All and vactor are the major manufacturers in the US. I'd suggest you contact a contractor and have them clean out the tank. It will be faster, and they will take care of dumping the contents.

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#10
In reply to #8

Re: Vacuum Truck

07/07/2008 8:41 PM

Thanks for all the answers. It seems that I should have given more info. Here it is .This is a centrifugal vac pump on a comercial sewage sucker which can pull 30"vacum on a 2500 gallon tank. The inlet for the hose is 4". Most of the time we use a 3" hose which is easier to manhandle when loaded. I am working for the contractor, who is fairly new to the business.We regularly lift solids from 20" below grade using both 3&4" hose in lengths of 33' We have also injected air from the truck compressor into the 4" hose at the suction end ONCE AGAIN Thanks to all Canuck 4

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#9

Re: Vacuum Truck

07/07/2008 10:25 AM

Look at this Sand and Mud Eductor link: http://www.s-k.com/pages/pro_01_06.html

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#11

Re: Vacuum Truck

07/07/2008 9:06 PM

Canuck 4

Reducing the pipe diameter will increase the velocity of the slurry though the friction head will also increase significantly. The only benefit of this increased velocity is to keep the slurry from settling and bogging the vacuum line.

If you can keep the concentration of solids (Cw %) below about 30% then you should not have any problems regarding the limiting settling velocity of the slurry with the 4" pipe (given a D50 particle size of .3mm).

I would look at trying to minimise the friction head losses and maybe go to a 5" or 6" pipe and try to keep the Cw% below about 15 %, these figures are extremely rough and require refinement.

I would keep adding water to the tank until all the sand is out.

Regards

Henry

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#12

Re: Vacuum Truck

07/08/2008 4:51 AM

If I reduce the suction hose to a 2" from a 4"will the volume be reduced and the velocity increased thereby making it easier to lift the product from the tank Thanks

No and yes, if you employ this device designed for the purpose...

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#13

Re: Vacuum Truck

07/08/2008 5:56 PM

Hello canuck4:

If by 'move the product' you mean you want it easier to move the hose without it getting stuck from the suction, perhaps the last metre of hose should be blanked off on the end. And other holes made say 100mm or higher from the end of the hose. This should stop the likelihood of the hose getting 'stuck'.

I do not know what type or shape of hose is available. I had a friend who welded some pipe of about 25mm internal dimension, using four lengths on the end so, it was level with the end of the hose. Then some 25mm rod was locked into the short lengths of pipe, it was past the end of the hose by about 200mm and, when most sludge was gone the rods could be withdrawn gradually allowing the last few drops to be sucked out. Of course this was 'home made' and, there may be various ends you can fix to the hose which are maybe made of a welded wire grill perhaps shaped to the shape of a ball?

babybear

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#14

Re: Vacuum Truck

07/10/2008 6:13 AM

A submersible pump suitable for dirty water would be a better bet, though the lift (~8m) might make a suitable animal difficult to track down.

A combination of that submersible pump and a vacuum lift truck might just do the trick, if pushed.

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#15
In reply to #14

Re: Vacuum Truck

07/12/2008 11:52 AM

We used the eductor/syphon for evacuating dirty water. The models we used could pass a six inch section of 2 x 4 board and pull 250 gallons per/min too.

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babybear (1); BigPete (1); BudT (1); bwire (2); canuck4 (1); chakraborty ranabir (1); dadw5boys (1); Del the cat (2); HarryBurt (1); Henry Crun (1); Just an Engineer (1); Mechanicalmark (1); PWSlack (1)

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