Question:
I am trying to pump a manhole that is about 30 feet deep and the truck is sitting up a hill about 10 more feet. What is the best way? It’s sucking but very slow and I don’t want to burn up the pump. Would a 2-inch hose work better than a 3-inch hose? Any suggestions?
Answers:
Maximum water lift at sea level is 33 feet. Changing hose won’t help. You’re near the limit of vacuum lift
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Try using a length of 3-inch PVC hooked to your hose. Make a 1/2-inch hole in the PVC so it will draw a little air.
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Can you drop a 3/4-hp sewage pump connected to a 40-foot drop pipe and pump it from below? Injecting air will help. The air will lower the density of the fluid, which requires less vacuum to lift the same distance. The air will also help keep the pump cool.
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You will need to lower the pump. With a 30-foot manhole you will need to get a pump lowered into the manhole. This is a problem if your pump is mounted on the truck. I hope you have a portable one. The only other way to do it would be to pressurize the wet well, but that would be harder to do.
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Take a 3/8-inch length of copper tube and hook it around the end of your hose with the end approximately 4 inches up inside the hose. Run the other end up the outside of your hose to the top. This is cheap and it works, allowing the product to ride up with the air.
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I had a customer with a deep sludge pit. I used a 4- by 4- by 1-inch PVC tee on the end of my 4-inch vacuum hose and I ran an air line back up and put a glad hand and a valve on the end, then hooked it up to my trailer brake line. Eventually I teed it into the air ride. It takes surprisingly little air to get things moving, and the pump has a much easier time.
A Mole in the Ground?
Question:
I installed chambers in a mound system. The soil has pushed up and filled the chambers. The chambers have not sunk because I uncovered all 400 feet and all elevations were OK. Also, the designing engineer did a perc test on the mound after lines were removed in undisturbed soil in the mound and the soil is rising there also. Does anyone know where I can get info on this?
Answers:
I am going to guess it is serious mole action. I now put cloth tightly around my lateral cleanouts because so many of the valve boxes got completely filled with soil. I don’t know how you would stop that in a chamber system.
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How long ago was the job done and where are you located? It could have something to do with frost heave.
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I disagree with moles or frost heave — we have seen this in Alaska where there are no moles. My completely unscientific input is that it’s very much like the dehydrated sponges you buy that “grow” the first time you soak them.
With virtually all leach systems except chambers, there is ground loading upon all of the infiltrative surfaces — the entire “receiving soil” has the weight of the earth above sitting hard upon it. Therefore, the weight of the ground above keeps this phenomenon from happening.
With chambers, the only ground loading that occurs is along the edges of the chamber — where it contacts the ground. The rest of the protected receiving soils area, the “void space” under the chambers, has nothing to force it to stay down. As the soils become damp, they expand slightly — not unlike frost heave but not necessarily freeze-induced. Over time this protected area has plenty of opportunity to expand, but little or no opportunity to dry out and settle again.
