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Water Pump Pulses On/Off for extremely short periods....


Bob Jones

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Hi Guys!

My excellent cheap water pump finally died after 5 years or so (Flow Max DS-01230-D2) so I installed a slightly used pump that I got off my neighbor because it was filling her fresh water tank over time. In my case, I have a high quality in-line check valve, so I was not concerned about her original issue.

The 'new' pump is a Shurflo 4008-101 which is a bypass pump design. It's working quite well, very quiet, and I've got it up to 75 PSI and working like a top. 

Only one thing. Every few seconds it very briefly pulses on then off. Just for a fraction of a second. This is when there is no water demand and the motorhome system has ZERO leaks. Ie, it will hold pressure forever. 

Any idea why it would pulse every few seconds for the briefest amount of time when there is no demand? 

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15 minutes ago, Dr4Film said:

Possibly it is leaking around the pressure switch?

It could be. I haven't run it long enough to see what's what. I might be worried about nothing since it's effectively a free pump. 

 

11 minutes ago, Todd P said:

Mine will do this if I need to change the water filters. 

I don't have water filters but it's an interesting idea since it would tend to indicate back-pressure could be causing it. 

I might have to just call the 'new' pump twitchy and ignore it 🙂 It did leak back into the fresh water tank on the unit I pulled it from but I do have a proper one way valve on the line so in my mind that really shouldn't matter. 

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I just replaced my 4008.  It developed a very small weep along the pump seal gasket. After 6 months of use (we full-time) it was happening more and more often… the weep finally developed into a small drip, so we found it and pulled it. 

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This was a very common occurrence on our houseboat.  All it takes is a small piece of dirt/sand in the check valve built into the pump itself.  You used to be able to disassemble the pump to clean the check valve, and they used to make a rebuild kit with all the diaphragms & such.  I'm not sure if the newer pumped can be taken apart & cleaned. 

When the check valve leaks, just a small amount, the water flows back into the fresh tank, so there is no external water leak.  The only "damage"is the pump running when it shouldn't, incurring additional wear & tear, and, if dry camping, it adds to battery drain. 

  - Rick N 

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I would consider reducing the PSI to 60 at the most. At 75 it may be pushing moisture out somewhere accounting for the pulse. And if so, a more serious problem will be just a matter of time. Either way,  it's worth the try.

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10 hours ago, waterskier_1 said:

This was a very common occurrence on our houseboat.  All it takes is a small piece of dirt/sand in the check valve built into the pump itself.  You used to be able to disassemble the pump to clean the check valve, and they used to make a rebuild kit with all the diaphragms & such.  I'm not sure if the newer pumped can be taken apart & cleaned. 

When the check valve leaks, just a small amount, the water flows back into the fresh tank, so there is no external water leak.  The only "damage"is the pump running when it shouldn't, incurring additional wear & tear, and, if dry camping, it adds to battery drain. 

  - Rick N 

That seems like a sound suggestion so I took the pump out and cleaned it up with compressed air etc. It was like new, and I can verify that the pump head is not leaking. I also pulled and cleaned the check valve. I sealed it up perfect and reinstalled it and....same thing 😞 

But at least I know the pump is 100% sound. 

6 hours ago, Chuck B 2004 Windsor said:

You might have a air bubble somewhere in the system.

It shouldn't be air as I'm pretty sure I've gotten rid of all of it. 

 

3 hours ago, Jim Wallace said:

I would consider reducing the PSI to 60 at the most. At 75 it may be pushing moisture out somewhere accounting for the pulse. And if so, a more serious problem will be just a matter of time. Either way,  it's worth the try.

I think I tried that already but can't be sure. I'll try again tomorrow. Also, I think I will check the pressure on my accumulator. It might be way off because this pump seemed to come on at a much higher pressure than the old one. 

I attached a video of what it is doing. That's why I call this pump 'twitchy'

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Could be the diaphragm opening and closing from a solenoid going bad. They have rebuild kits for that but it's probably easier to just replace.  I can't tell if water is actually being discharged through those pulses. You could pull the head off and inspect that nothing is loose inside. 

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If there is no leak in the system, you most likely have a situation where the pump is bleeding back into the fresh tank. The best way to solve that is to cut the pex coming from the fresh tank to the pump and install a Sharkbite check valve in that line. That solved the problem for me.

 

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On 10/3/2022 at 9:00 AM, Dr4Film said:

You get what you pay for!

Hopefully it was FREE, what else can we say.

It was free! In fact, the old owner (the widow across the street) was just over for coffee and I told her that the folks down in the states told me I should ask for a refund! 🙂

On 10/3/2022 at 10:14 AM, Doug and Nicki said:

If there is no leak in the system, you most likely have a situation where the pump is bleeding back into the fresh tank. The best way to solve that is to cut the pex coming from the fresh tank to the pump and install a Sharkbite check valve in that line. That solved the problem for me.

 

MODERATORS EDIT.

After researching, the pump and water system is maladjusted and not operating within the manufacturer’s specifications and operating instructions.  It is recommended that the system be returned to such.  One of the tenets of the forum is to prevent future readers from misinformation that could damage the MH or cause injury.  It is recommended that the settings be returned to the normal operating range and then advise if there are still issues.

That was why it was originally removed from service. It was effectively new but the fresh water tank was self-filling. So I installed a new pump for her and took the old one with me as a spare. I had already installed a nice brass check valve on the line for just such an occasion. 

Today I readjusted the pressure in the accumulator as it was way off. With the old pump, which came on at 40 PSI, I had the accumulator at 38 PSI. I have the 'new' pump set up to come on at 52 PSI and shut off at 76 PSI. So the accumulator is now @ 50 PSI and the pump, of course, still does it's little twitch. 

Nice pump, otherwise. Very nice. Quiet and powerful. Zips right up to 76 PSI without a complaint. Mind you, it's being fed good power. 

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On 10/3/2022 at 11:54 PM, Bob Jones said:

So far it's been a better performer than regular unit - albeit a bit twitchy. Mind you, those twitches seem to keep the pressure right up there. My toilet gives a loud whoosh. As you said though, it was free. And it sure is quiet. 

You might be “pumped up a little TOO Much”,  I can’t remember the warnings but somewhere think that 60 - 65 is the normal range for the Remco AquaJet 55 series,  maybe an operating range of 45 ON and 65 OFF with an accumulator set at 43.  Have not read all the pertinent details, but never remember hearing of folks having pumps set that high,  you get a lot of excess flow which equates to tanks filling up more often, not to mention excess stress on the system.  Most of the adjustable RV regulators with pressure gauges are factory set to 55 PSI

If you Google Normal RV Pump Water pressure, you typically get 40 - 60 PSI.  And that is on many sites

https://rvshare.com/blog/12v-rv-water-pump/

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No doubt you have tested your system and your past comments on troubleshooting and such indicate an innate knowledge of it.  However, one of the rules or tenets of this forum is to make sure that information that could be misinterpreted by future readers or those that do not have a certain level of expertise are aware when something is posted or recommended that is not in accordance with good, safe or normal operating parameters is marked as such.  here is the text from your Shurflo 4008-101 manual. 

NOTE: By-pass adjustment should only be performed by a professional techni- cian with proper gauges and equipment.
The by-pass is a spring loaded dia- phragm that opens up allowing water from the discharge side back to the inlet side. The by-pass is set to begin opening at about 40 psi and creating full by-pass at about 62 psi (lower pressure pumps will vary depending on the by-pass and pressure shut-off settings). The pres- sure switch on the pump is set to shut off at 55 psi. If the switch or by-pass
are adjusted too much, the by-pass and switch shut-off can overlap and THE PUMP WILL NOT SHUT OFF. Screwing the switch screw in clockwise will raise the shut-off pressure. Unscrew- ing the switch screw counterclockwise will lower the pump shut-off pressure. Screwing the by-pass screw in will raise the pressure at which the by-pass starts and raise the full by-pass pressure. Unscrewing the by-pass screw coun- terclockwise will lower the pressure at which by-pass starts and lower the full by-pass pressure.
WARNING: If full by-pass is reached before the shut-off setting, the pump will not shut off. Full by-pass pressure setting should be at least 10 psi

https://www.pentair.com/content/dam/extranet/web/nam/shurflo/manuals/911-1008-4008-rv-by-pass-pump-iom.pdf

Typically when members want to experiment, we have sometimes asked them to take such offline with other likeminded members  as the posts might be misunderstood and then someone without the knowledge will  damage their MH or injure themselves 

Therefore, your previous comments will be edited to reflect that the pump and your system is operating outside the owner’s manual specifications.

Thanks for understanding.  

 

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9 hours ago, Bob Jones said:

I'm sure, but when I was trying out those Remco's one of them hit 110 PSI. That was nice!! I have faith in my plumbing 🙂

Yikes, 110 psi, I hope that was only a test!!!.   I'd be worried about all the connectors and fittings in the system, it's the weakest link that will get you. 

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9 hours ago, Bob Jones said:

I'm sure, but when I was trying out those Remco's one of them hit 110 PSI. That was nice!! I have faith in my plumbing 🙂

 

49 minutes ago, jacwjames said:

Yikes, 110 psi, I hope that was only a test!!!.   I'd be worried about all the connectors and fittings in the system, it's the weakest link that will get you. 

I think I read somewhere that the PEX and fittings in our Monaco coaches are rated for 100 psi. So, at a 110 psi I would expect leaks to occur somewhere. 

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