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Dry pit pump

Dry pit pump

(OP)
We have a old Smith and Loveless below grade "can" type duplex raw sewage pump station (20 hp each). The existing pumps are so old and therefore needs replacement. My first thought was to use dry pit close coupled submersible (By Sulzer, Xylem) but can we also consider dry pit sewage pumps that are air cooled? Apart from Hydraulics, piping and electrical which I am familiar with what are the other critical factors that needs to be looked at when considering dry pit sewage pumps in this situation?

Thanks in advance.

RE: Dry pit pump

One of the factors that may drive your decision whether or not to use dry mounted submersible pumps is whether there is any risk of flooding your pumpstation. When i say flooding i mean from any source be it weather related or a process problem , or a simple operational mistake.
Dry mounted submersibles are relatively safe against flooding provided the electrical work is done correctly. Dry mounted submersibles are normally lower rated than the submersible equivalent because of the lower amount of cooling available by not sitting in water. However there are some brands that add an extra water jacket to the pump and motor and circulate some of the pumped fluid through the water jacket. Others use a seperate cooling water supply to achieve the same end.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Dry pit pump

One aspect that should be addressed is that those old can lift stations are confined space and no longer acceptable.

The lift station is probably so old anyone that the steel can is corroded. Steel lift stations are generally good for 20 years or so. The controls probably are shot as well.

Rather than replacing the pumps, you should replace the entire lift station.

RE: Dry pit pump

(OP)
Bimr,

Fully agree about confined space. Actually we are planning to raise the controls out of the can to the grade and installed in a weatherproof enclosure. Our utility is expecting to see some land development taking place in the vicinity during the 3-5 years time and want to get the developer to construct the brand new PS replacing the existing and therefore want to defer the structural replacement.

ashtree: When you say "Dry mounted submersible" are they the same as "Dry pit submersibles"? I know that dry pit subs have cooling jackets.

This pump station has been in service for the last 30 years or so and the S&L pumps (I heard that S&L used some other manufacturer's units)are very old and have survived all these years without any flood relate issues. I have not been able to trace the original specs. as the city's utility department has changed hands many times and the documents lost during the transition.

RE: Dry pit pump

Yes , i think we mean the same thing just different terms.
And yes you are correct in that many if not most have cooling jackets in the 20hp size.
If you are planning to retain the can as is i am not sure how you intend to use the dry mounted pumps. Normally these would sit in a dry well beside the wet well seperated by a wall, but are you considering installing these above the normal operating level. If you are you will need to go to a totally different style of pump because you cannot use a foot valve on the suction.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Dry pit pump

(OP)
ashtree, the current pumps are flooded suction. There are two independent suction pipes coming from wet well with isolation valves feeding each pump. I will be working with pump manufacturers to get a pump to fit the existing arrangement. The space in the can is tight but we will replace the inside piping as well which might give us some additional room.


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