Question:

I have a customer who wants to put a check valve after the tank, inside the pump chamber to prevent basement flooding in the event of high water table and pump failure. I can get one, but it is so big (designed to have pipe at either end and measures at least 9 inches) I will have trouble putting in a pump. Does anyone know of a narrow check valve designed to go in that location that won’t take up half the space? Ideally it would be a flapper with only one socket for a glue joint.

Answers:

They are huge. You can dig down and put it outside the tank. The one I use has a threaded top to access the guts so you can put a 4- or 6-inch pipe on it for a riser.

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Why not put a high-level alarm in the pump vault so he knows when the pump fails? If he is worried about flows back into the house maybe put the backflow valve upstream from the tank? In any case, the vault and tank should be watertight so no infiltration from outside should get in and the dispersal field should be in a location where it is above high water table. (Various jurisdictions have regulations regarding vertical separation from the infiltrative surface to seasonal high water table.) A check valve should be located on the force main from the pump, inside the vault, so no water can get back into the vault.

I prefer a rolling ball check valve, as I have had problems with the flapper type. I have had the rubber hinge on the flapper tear off so the disk inside is loose, then it can be forced up, sometimes just right, so it closes the outlet from the valve. So the pump runs but won’t pump.

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They are common here where we are all below the river level every spring. But come to think of it, most of the homes have them in the basement. That would be a lot easier.

Vane vs. Blower Pump

Question:

Can anyone explain in regular terms the difference between how a lobe blower such as a Roots blower and a vane pump works? We are in the sewer cleaning business and have Vactor and Clean Earth trucks with blowers, but just bought a straight vacuum truck to venture into the septic pumping business. It too has a blower (It came from a company that used it primarily for industrial pumping.), but I was told that it would not work for septic tanks and that a vane pump is better.

Answers:

To answer the first part — basically a lobe blower uses two rotors that rotate together at high speed to create the vacuum. A vane pump uses vanes that rotate around inside of a housing creating a seal gap that does the job. A vane pump burns oil; a blower uses oil to lube gears but does not burn it.

For septic, vacuum is vacuum. It doesn’t matter if you have a blower that produces 27 inches Hg with a 200-cfm flow or a vane pump that produces 27 inches Hg with a 200-cfm flow.

Blower advantages include sustaining high vacuum for unlimited periods of time without overheating. Blowers do not burn oil and have no emissions other than heat. Disadvantages include cost, and if they crash, they’re usually not repairable.

Vane pump advantages include cheap startup cost and ability to repair easily. Disadvantages include use of oil, requiring you to refill the reservoir. The oil is exhausted into the atmosphere. Heat during high-vacuum levels could get out of hand if run for extended periods of time.

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In addition, I have received the following from owners and operators:

Vane pumps offer a lower initial investment, but are much more expensive to maintain. I have been told that the vanes need to be replaced annually at a cost of about $1,000. As the vanes wear, your performance decreases. I have also heard that they are loud and messy.

Positive displacement blower pumps are much more reliable, typically lasting 10-plus years with little maintenance. Unfortunately, they require a larger initial investment. They are usually smaller and lighter for the same performance, but require a good filtration system and a set of silencers.

Usually the flow rate determines the equipment. If the flow rate is low enough, the vane pump is the best solution. As the flow rate requirement rises (600 cfm at 18 inches Hg), the vane pump and blower pump performances will overlap. I think most would agree that once you get into the overlap scenario, the blower pump is the best solution.