Sump pump question 3

[Lan123]

I am trying replace some exsiting sump pumps( 4.5 ft in diameter). Sump collect drainage water. For a submersible sump sump (5hp), what should be the maximum starts per hour. I always thought that that this was 6 but I was told that for a smaller pump like this starts can be increased upto 15 starts per hour.

If I increase the starts what precautions should I take to cool down the motor. Should I keep the motor submerged all the time

Also for a small sump pump duplex system that uses floats what should be the recommended depths for the following

1. Depth between the lead pump on and lag pump on? 6"
2. Depth between lag pump on and the high water alarm 6"
3. Depth between the High water alarm and the lowest invert 6"

Thanks in advance

 

[MJCronin]

Lan...

The maximum number of starts per hour is a function of the heat rejection of the pump. Submersible pumps must reject heat into the surrounding liquid. The maximum number of starts/hr must come from the pump vendor.

As a general rule of thumb, smaller pumps can sustain more strts per hour than larger pumps (with motors that generate more heat).

In my experience, I recall numbers from 4 to 15 starts/hr...

-MJC

 

[bimr]

The object is to limit the number of starts per hour the pump makes. The larger the motor, the fewer starts are recommended. Franklin recommends up to 300 starts per day for 1/2 and 3/4 HP motors, 100 per day for 1 HP thru 5 HP, and 50 per day for anything up to 30 HP.

You will need to contact the pump manufacturer for more specific information.

Grundfos for example states a Maximum of 20 starts per hour, evenly distributed once every 3 minutes.

http://www.us.grundfos.com/web/download.nsf/Pages/B776A306439A6DA9882567620062ED3B/$File/Qf-sse.pdf

 

[21121956]

Hello everybody:

Lan123, for your question #1 and #2 the distance is 1 feet and 0 inches, minimum.

Normally, for average daily flow conditions, the cycle time (the time the pump is at rest + time of pumping out) is 30 minutes.

For peak flow conditions it is recommended to have a cycle time above 10 minutes (some designers select 15 minutes, which means 4 starts/hour).

As a general rule, most of the pumps manufacturers recommend no more than 10 - 12 starts/hour per pump, working under peak flow conditions.

El que no puede andar, se sienta.

 

[cbrenier]

Also, keep in mind single phase motors typically have integral thermal overload protection, which has a life span. It is imperative to ensure the amount of cycles during peak conditions is also considered as much as the actual run time of the cycle. As to not activate this protection on a normal basis. Exhausting and relying on the overload protection to "time-out" the pump will result in a short pump life.

Take into account, the amount of volume per inch or foot, the expected equilibrium point on the system curve (GPM) for optimal cycle time, rest and as a result life of the pump!

Unfortunately, there is no rule-of-thumb for float switch elevations. This will vary from application, and depends on physical size of the pump, volume of basin per foot, expected GPM, desired run time, desired rest during peak conditions. In addition, in regards to the alarm, there should be absolute room from the alarm to the inlet to allow proper response of the problem.

 

[Artisi]

The number of starts per hour specified by the manufacturer will be a conservative number - bear in mind they have to cover their backside so will naturally set the number very low.
like most things in life the number of starts per hour is a considered judgement based on many factors - how often will the pump need to make closely spaced multiple starts, all day every day, or a few times a day during peak conditions - what is the temperature of the water - is the pump fully submerged when starting and operating etc.
If you want to exceed the maximum number of starts per hour and I don't see any good reason not to, within limits of course, make an informed decision and try it. Most quality sump pumps include some form of thermal o/load - so if it isolates the pump you know you have exceeded the limit - rearrange the timing in this case.

I've seen sump pumps cycling on and off for hours due to faulty float switches etc without any great drama as the thermal o/load has taken care of it - ok, maybe it shortened the life of the thermal switch but the pump motor didn't burnout and survived.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[SteveWag]

This is not on target, but for what it may be worth:

For many years the BIF Corp had flowmeters, as well as other devices, with a pulse output. The pulse repeated every 15-seconds, three seconds of OPEN followed by a contact closure of 0 to 12-seconds, with 0-seconds equaling 0 GPM and 12-seconds equaling 1500 GPM. This whole scheme was for transmission over telephone lines.

I was called to look at a fluorine feed problems. Arriving at the site, I found a 5-HP three-phase motor driving a fluoride feed pump. Some years past someone wired the 15-second pulse so as start a Square D motor starter. So this pump started every 3 + 4 or 5 seconds, ran for up to total of 12-seconds and stopped and repeated. This was an older “U” frame motor that started every 15-seconds all day, all year. It was 4 or 5 years old when I was introduced to it and that first time the problem was burnt (missing) contacts. This was 1972 and I replaced ONLY contacts until the feeder was taken out of service in 1993. I saved the motor and it powers a drill press now, using the same motor starter and thermal overloads.
Steve