Sump Pump Switch MTBF - Plumbing - DIY Home Improvement | DIYChatroom


Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Plumbing

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Display Modes
Old 07-18-2010, 10:08 PM   #1
Newbie
 
Join Date: Aug 2009
Posts: 20
Rewards Points: 10
Default

sump pump switch MTBF


Talking sump pumps in another thread got me to thinking. Most home owners use a 1/3 to 1/2 HP 1 1/2" submersible style pump. I use a Zoeller M53 with mechanical switch. During spring heavy rains my pump can run every 30 seconds for days on end. Once the water table settles down it may come on a few times a day as ground water seeps in. During the dry months it never runs. During the winter, it runs very little. Adding up all the cycles throughout the year I would say it sees 250,000 cycles per year. A conservative estimate. I have a very expensive finished basement that this pump protects. If it goes down during the rainy season I would be in big trouble. Therefore, I replace it every three or four years just to be safe. I'm thinking a million cycles on the switch makes me nervous, but I bet in their test labs they go 4 or 5 million.

I looked on the Zoeller website and could not find any documents that show cycle failure rates. I'm sure they know how many average cycles their mechanical swithes can run before failure. Does anyone know?

Advertisement

rustyedge is offline   Reply With Quote
Old 07-18-2010, 10:17 PM   #2
Member
 
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000
Default

sump pump switch MTBF


Quote:
Originally Posted by rustyedge View Post
Does anyone know?
The switch OEM.
You can prolong switch life with an arc-suppression network or oversizing the switch.

Ask if the most common failure mode is for the contacts to weld together or to have increased contact impedance.

You could use a separate water level alarm. Failure rate calculations involve exponents and the answers are sometimes counterintuitive; without knowing the MTBF of the whole pump I can't say what level of reliability a four year replacement scheme buys you.
I can tell you that CO detectors have a 99% chance of working when new and that aircraft level reliability has 1 chance in a million of failure, "six nines" reliability, 99.9999%.

http://en.wikipedia.org/wiki/Failure_rate

http://www.google.com/search?hl=en&s...=&oq=&gs_rfai=

If a pump costs $500 and basement repairs cost $5000, the pump should have a reliability over your time interval of interest of at least 1-(500/5000) = 0.9 = 90%.

Advertisement


Last edited by Yoyizit; 07-18-2010 at 10:37 PM.
Yoyizit is offline   Reply With Quote
Old 07-18-2010, 10:35 PM   #3
Newbie
 
Join Date: Aug 2009
Posts: 20
Rewards Points: 10
Default

sump pump switch MTBF


My installation does have a high level alarm, a water jet back up plus a 12 volt back up I can run off my car battery through an access door cut through the wall that leads to the garage. I've been using Zoeller pumps with the built in mechanical switch for over 20 years and have never had a failure, but then again I don't run to failure. I'm just curious as to what their standard switch cycle life may be.

I have also seen after market piggyback switches with high quality micro switches inside like the Rhombus vertical master and a new one I saw that triggered the pump when two electrodes touched the water. I would think these would be very reliable also.
rustyedge is offline   Reply With Quote
Old 07-19-2010, 07:30 AM   #4
Member
 
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 6,976
Rewards Points: 2,048
Default

sump pump switch MTBF


Any chance you could put in a bigger or deeper pit? Or a second pit next to the first with a large interconnection pipe at the bottom?

Or a second pit with a backup sump pump in it? If the second pit is not connected to the first for example is in the opposite corner of the basement, the float switches should be adjusted each year so the second pump kicks on first every other year.

If your pump is kicking on ever 30 seconds or so, chances are that accumulating more water before starting to pump it will give just as good performance while prolonging the pump life with fewer starts and stops.

If it is just the switch you are concerned about, you could install a second set of floats with a second switch connected to the same pump, and manually trip each switch every month or so to see if a switch needed to be replaced.
__________________
Forget super sized fries. The Washington Redskins could promote healthy eating with First Lady Obama by choosing a (red skinned) turnip for a mascot.

Last edited by AllanJ; 07-19-2010 at 07:53 AM.
AllanJ is offline   Reply With Quote
Old 07-19-2010, 10:18 PM   #5
Newbie
 
Join Date: Aug 2009
Posts: 20
Rewards Points: 10
Default

sump pump switch MTBF


A bigger or second pit and pump would really be the way to go but that is really not practicle. Everything I have works good and is reliable, just during the rainy season the pit can fill and empty pretty fast. All the water coming in comes through the dozens of 3/4" holes drilled into the basin itself. Nothing comes from the perimiter drains. I guess due to the downspouts being trenched to the back of my property and not a lot of water actually gets to the foundation.

I do like the idea of a secondary back-up switch. How would that work? Would I need a new pump? One without a built is switch?

Thanks for replies.
rustyedge is offline   Reply With Quote
Old 07-19-2010, 10:28 PM   #6
Member
 
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000
Default

sump pump switch MTBF


Quote:
Originally Posted by rustyedge View Post
I do like the idea of a secondary back-up switch. How would that work?
Paralleling or series config. for two switches using the same pump depends on the likely failure mode for the switches.
If the contacts are likely to weld put them in series. If the contacts degrade to a high impedance put them in parallel.

If each switch has a failure likelihood of 1% (.01) then two would have a likelihood of .01^2 = .0001, 1 chance in 10,000.
Yoyizit is offline   Reply With Quote
Old 07-20-2010, 06:55 AM   #7
Member
 
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 6,976
Rewards Points: 2,048
Default

sump pump switch MTBF


You would need some mechanical skills (to mount the second float assembly to the side of the pit or to the existing pump) and some electrical skills (to wire in the second switch in parallel with the existing switch on the existing pump).

It may be possible to put the second switch on the original set of floats, but here you lose the protection against float mechanical failure.

(For those of you with Ph.D.'s in electrical engineering, including one here whom I won't name) This will avoid having the pump run continuously and burn out and also avoid failure to come on, all due to bad switches, unless you have incredibly bad luck where multiple switches fail at almost the same time. Have the two sets of floats. Have four switches, two on each set of floats that will activate together. The two switches on each set of floats are wired in series; the two sets thus configured are then wired in parallel. To do your monthly test, start with all switches in their off positions. Flip both switches on one float set using your fingers. If the pump does not come on, then at least one switch is stuck off; pull that float assembly out and replace the switches. After those tests, flip each switch individually. If the pump comes on, then the other switch on that set is stuck on; replace it (suggest replacing both or even all four switches for peace of mind).
__________________
Forget super sized fries. The Washington Redskins could promote healthy eating with First Lady Obama by choosing a (red skinned) turnip for a mascot.

Last edited by AllanJ; 07-20-2010 at 07:16 AM.
AllanJ is offline   Reply With Quote
Old 07-20-2010, 02:32 PM   #8
Part time DIYer
 
Join Date: Feb 2010
Location: Saskatchewan, Canada
Posts: 4
Rewards Points: 10
Default

sump pump switch MTBF


I conduct MTBF(Mean Time Between Failures) calculations for electronic systems at the company where I work.

Every switch will have its own specific MTBF that only the manufacturer would know. Unless they have given it out and most are willing.

As a standard there are ways to estimate the MTBF when it is unknown. As stated above this usually involves math.

One resource that would be useful (and is available free online) is the Military Handbook 217F, Reliability Prediction of Electronic Equipment.

Specifically section 14.

You can google this resource. it is a 80 page PDF.

Without knowing your switch specifically I had to do some educated guessing and it look like a higher quality switch should have a failure rate of less than .001 or a MTBF of 1,000,000,000,000 hours.

Now you may notice that the MTBF is given in hours. That wont help you too much as a switch is not operating continually like most electronic components. You are not looking for the MTBF but you are looking for the life of the switch. This would be rated in number of cycles.

The best bet would be to contact the mfg and ask about the number of cycles in the life of the switch.
arcangle is offline   Reply With Quote
Old 07-20-2010, 05:06 PM   #9
Newbie
 
Join Date: Aug 2009
Posts: 20
Rewards Points: 10
Default

sump pump switch MTBF


Well I did some research today. I dug through the Zoeller site looking for life expectancies. They only thing they say is 7 to 10 years of normal service, whatever 'normal' means. Is that 10,000 cycles? 100,000? A million? Who knows? I sent them an email. If I hear something I will repost.

The good news is Watchdog makes a real nice dual float piggyback switch for about $40. My plan now is in another year or so I will replace the automatic pump with a non-auto and use the dual switch. I may even buy the watchdog brand pump. This way the float can be adjusted to make the water level as high as possible which will cut the short cycling I now have a little bit.

Thanks for the replies. I have learned a lot from this forum.
Attached Images
 
rustyedge is offline   Reply With Quote
Old 07-20-2010, 05:27 PM   #10
Member
 
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,990
Rewards Points: 2,000
Default

sump pump switch MTBF


You could also monitor closed switch voltage right at the switch terminals when the motor is running and watch the contact resistance increase as the months go by.

Generic pass/fail limits are less than 30 mV is good and more than 100 mV is bad.
Yoyizit is offline   Reply With Quote
Old 07-20-2010, 06:18 PM   #11
Member
 
Join Date: Nov 2007
Location: Nashua, NH, USA
Posts: 6,976
Rewards Points: 2,048
Default

sump pump switch MTBF


I forgot to mention, if the perimeter drain pipes are not in a bed of pea sized or larger gravel, the drainage part of the system will stop functioning when the pipes fill up and you can get seepage and wicking of water up onto the basement floor, probably starting at the opposite corner. Since you probably don't know how the perimeter drain trenches were constructed, you play it safe by having the pump come on before the ends of the drain pipes as seen in the pit get fully submerged.

If the perimeter drain trench is gravel filled, then it will keep functioning until the water level gets to the top of the gravel, filling all the air spaces.

Finding out how high you can let the water rise before the pump kicks on and without getting any flooding is a trial and error process.

A switch that uses two electrodes to sense the rising water will let the pump shut off after just a few seconds of on time when the water level drops slightly. That is, unless there is a built in timer that keeps the pump running for a fixed time interval whether or not the pit is emptied out.
__________________
Forget super sized fries. The Washington Redskins could promote healthy eating with First Lady Obama by choosing a (red skinned) turnip for a mascot.

Last edited by AllanJ; 07-20-2010 at 06:30 PM.
AllanJ is offline   Reply With Quote
The Following User Says Thank You to AllanJ For This Useful Post:
rustyedge (07-20-2010)
Old 07-20-2010, 07:41 PM   #12
Newbie
 
Join Date: Aug 2009
Posts: 20
Rewards Points: 10
Default

sump pump switch MTBF


Quote:
Originally Posted by AllanJ View Post
I forgot to mention, if the perimeter drain pipes are not in a bed of pea sized or larger gravel, the drainage part of the system will stop functioning when the pipes fill up and you can get seepage and wicking of water up onto the basement floor, probably starting at the opposite corner. Since you probably don't know how the perimeter drain trenches were constructed, you play it safe by having the pump come on before the ends of the drain pipes as seen in the pit get fully submerged.
I do know the perimiter drains are properly installed with gravel. I just don't think they see any water because the downspouts are trenched and the clay soil around here. Plus the ground is sloped away from the house for the most part. Like I said, the water in the sump pit is strictly ground water from the water table rising when it rains.

Before I finished my basement I did play around with filling the sump to the point where I would see water come in the basement but I never fully followed through. I wish I would have now. When I do eventually install the new float and pump, I will probably have the pump kick on when the perimiter drain pipe is about 1/2 full.

The Watchdog website had several nice items. The dual float switch plus a new silent closing check valve. Another good idea.
rustyedge is offline   Reply With Quote
Old 07-21-2010, 12:00 PM   #13
Newbie
 
Join Date: Aug 2009
Posts: 20
Rewards Points: 10
Default

sump pump switch MTBF


I did hear from Zoeller, Watchdog and Rhombus. Zoeller says their switches are a 100,000 cycle switch. 50 pump cycles per day would be about a 5 1/2 year service life.

Watchdog says their dual float switch has been tested 250,000 cycles without failure.

Rhombus vertical master switch is also tested to 250,000 cycles.

I figure my pump could see as high as 40,000 cycles per year but realistically probably 30,000 max. Changing mine out every 3 yrs I guess turned out to be a good idea.

Advertisement


Last edited by rustyedge; 07-21-2010 at 02:19 PM.
rustyedge is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sump Pump issue - New home owner RockWood610 Plumbing 8 09-08-2009 01:21 PM
Sump Pump Electrical Problem loftezy Electrical 5 09-06-2009 07:14 PM
Sump Pump Questions henlij Plumbing 19 08-12-2009 08:50 PM
sump pump issue mikehende Plumbing 15 02-15-2008 07:36 AM
Foundation drain and sump pump slatergrl Plumbing 3 02-10-2008 10:36 AM




Top of Page | View New Posts