Please help me find a "gentle" pump for a septic system dosing tank. 4

[InSite]

I am designing a residential, gravity dosing septic system. Due to the close proximity of the dosing tank to the d-box and the small elevation difference, the pump only needs to work against ~6' to 7' of total head. I found one pump on the internet (Barnes) which yields a flow of ~38gpm at my head, but it's 2HP. I'm thinking it's better for the homeowner to have a 1/3HP or 1/2HP pump instead. The best I can find on the internet at those HP's yields ~80gpm, which translates into ~3.7fps discharge into my d-box.
That's the situation - Here's my questions:
1) Can anyone point me to a more appropriate pump? Or,
2) In any case, I am employing an elbow at the inlet of the d-box to shoot the effluent to the bottom of the d-box. If I use the pump with 80gpm discharge, should I be concerned about wearing away the bottom of the concrete d-box (3" discharge pipe at ~3.7fps and ~4" above the bottom)? Should I use some sort of plate? If so, what type of material is advisable to resist the corrosive effluent?
Thanks very much in advance for all your help!

 

[RWF7437]

You might consider using small grinder pump(s). A company callws Environment One specializes in these, as I recall. Try a web search.

good luck

 

[RWF7437]

Here's the link:

http://www.eone.com/

 

[semo]

I would look to the manufacturers of "septic tank effluent pumps". There are numerous ones out there. You want to find a pump whose pump curve meets your requirements.

Since this fluid will not have solids in it, you can also modify the piping (partially closed valve, restrictions/enlargement, etc.) to make your pump operate at a different point on its curve.

I would recommend you find a pump curve that meets your situation. This sometimes means looking at numerous pumps.

As far as the HP goes, you are looking at the rating. The pump will only use as much energy (HP) as is required to perform the work you are asking. Looking at the pump curve and seeing where it operates in your situation will tell you how much energy it will use. Various pumps have various efficiencies which also influence this. I would not worry about having a 2 HP pump.

Since I don't have your design flow, the equation to calculate the horsepower needed is as follows:

HP = Flow(gpm) * Head (ft) / 3956

Dividing this by the pump efficiency and then by the motor efficiency will give you the input horsepower. The actual motor horsepower used will be higher than this because of manufactured sizing and safety factors; but, this is the energy the pump will use.

 

[greatwhitenorth]

at this Q/TDH, there is no sense in using more than a 1/3 HP pump. Myers, Zoeller, Goulds all make a suitable effluent pump. You can reduce exit velocity by expanding to a larger diameter pipe at the d-box (v=Q/A). There are also plastic D-boxes that have a "well" below the outlets to quiet flow.

I would not recommend a grinder pump.

In general, a d-box is a crude method of flow distribution to laterals/trenches. By far the most accurate method to date is a pressurised distribution system (no d-box) - see Washington State guidelines for pressure distribution.

Failing this, I would use reducer tees and pipe straight into the various trench pipes. In both methods, discharge rate to a lateral is a function of pipe or orifice diameter and head pressure.

 

[InSite]

Thank you all for the valuable information - you have provided very insightful guidance.

 

[erikfinley]

http://www.hydromatic.com/

SHEF40 is a pretty common pump used for effluent in low head situations.

 

[DrRobS]

You could try a company in the UK called Pump & Package Ltd. They should stock, or if not be able to source a pump such as this. They are contactable on 01536 762764.