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Old 04-02-2008, 06:31 PM   #1
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I just had my second Shurflo 5.7 pump fail on Monday. I took it to Shurflo to get it checked, and they replaced it. I also had them check the previous bad pump, and the technician said both suffered from the same failure: Too much back pressure.

He suggested a check valve between the pump and the water heater. I thought the water heater had a pressure relief valve on it to release the pressure buildup as the water heats and expands. Am I mistaken?

Anybody know if there is a check valve in the system already? Should there be?? I had 20 years with class C motorhomes before the Alpine Coach and never had a pump fail. Granted they were lower flow systems and not pushed as hard.

I see the Shurflo 5.7 pump has horrible reviews on the Camping World website. I am not sure if they relate to my experiences.
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Old 04-02-2008, 06:31 PM   #2
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I just had my second Shurflo 5.7 pump fail on Monday. I took it to Shurflo to get it checked, and they replaced it. I also had them check the previous bad pump, and the technician said both suffered from the same failure: Too much back pressure.

He suggested a check valve between the pump and the water heater. I thought the water heater had a pressure relief valve on it to release the pressure buildup as the water heats and expands. Am I mistaken?

Anybody know if there is a check valve in the system already? Should there be?? I had 20 years with class C motorhomes before the Alpine Coach and never had a pump fail. Granted they were lower flow systems and not pushed as hard.

I see the Shurflo 5.7 pump has horrible reviews on the Camping World website. I am not sure if they relate to my experiences.
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Old 04-02-2008, 11:21 PM   #3
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Jim - "Too much back pressure" in the RV doesn't make sense to me. I have to wonder if it may be a 'standard line' given for failures. Keep in mind, RV pumps are designed to turn off when back pressure builds up. Notice how they turn on when you switch the pump on, until pressure builds up. This build up of pressure is back pressure. Then they turn off automatically, by design, when sufficient pressure builds. Quite honestly, I suspect some different cause of the problem.
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Old 04-03-2008, 03:47 AM   #4
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Oddly enough the 5.7 pump is by far the best pump I have ever had in over 30 years between our boats and motorhomes and I have never had to replace or repair any of them.
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Old 04-03-2008, 04:18 AM   #5
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Jim and Steve,

This might make a lot of sense. When the water in the water heater heats up, it expands. If the pump is shut of at maximum pressure at the time when the water heater comes on, them the pressure in the system could raise quite high. The check valves built into the pumps are only rated for a certain amount of pressure. The installation for the AquaHot system, calls for an expansion tank in the hot water system for just this situation. This would occur the same way with any water heater. As to SteveS's comment "I have to wonder if it may be a 'standard line' given for failures" I have found ShurFlo to be very straight forward and accommodating in regard to solving any problems with their product's. Why it would only effect the 5.7 pumps, I don't know. I do know by personal experience and conversations with others, that the later 5.7 pumps have had many problems, although as Ted and many others have stated, some of them have worked perfectly and when they do they are great pumps.
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Old 04-03-2008, 06:00 AM   #6
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As an added note to the above. Jim, the pressure relief valve on water heaters are set to release at quite high pressure, like when a thermostat fails and steam is produced. There is a large difference between the working limit on the pump check valve and the setting on the water heater pressure relief valve.

My cure for my problems, was to add a 2 gallon accumulator tank, which is basically an expansion tank. I am wondering if the small tank that Shurflo makes would have been enough, it the problem was due to this pressure build up? Each time the pump was replaced or worked on, it would work good for a while before acting up and the old one was not checked by ShurFlo tech's.
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Old 04-03-2008, 06:16 AM   #7
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Why does this pressure buildup only cause the 5.7 Shur-Flo models to go bad, and not other model Shur-Flow pumps.

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Old 04-03-2008, 08:37 AM   #8
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Only a guess, but could it be due to the variable flow design of the pump. The early 5.7 pumps had a different pressure sensing design than the later ones. The new ones have an adjustable pressure switch. Also might be if the 5.7 pumps cut off at a higher pressure, who knows?
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Old 04-03-2008, 11:39 AM   #9
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Jim,

WRV replaced the Shurflo 5.7 pump while we were there a couple of weeks ago. It is our third Shurflo pump since May, 07. Makes you wonder why, doesn't it?.
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Old 04-03-2008, 03:40 PM   #10
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Why doesn't someone write a letter to Shur-Flo and explain that quite a few motorhomes have had problems with the 5.7GPM pumps. If they indicate that it is back pressure (which makes no sense to me)ask them to explain it and what to do about it.
They know there are other pumps on the market.
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Old 04-03-2008, 05:56 PM   #11
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I am sorry to not get back to this discussion I started sooner.

The technician told me that to cause the failure mode he found, the back pressure had to be at least 250 psi. I would think with this kind of pressure I would have noticed a spurt when I opened a faucet. Which I never noticed. I find it hard to believe that the pump would be the weakest link in the system at that pressure.

The technician did tell me what Shurflo suggests to do about it. He said to install a check valve before the water heater.

Anybody have any experience with the Flojet Sensor VSD 4.5 gallon per minute pumps. The CW website gave it very good reviews, far better than the Shurflo 5.7. I hate to downgrade the water system flow, but if the pumps last longer, it might be worth it. We don't have a washer/dryer to use a large amount of water. Just the shower.
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Old 04-03-2008, 07:37 PM   #12
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Ditto, I just replaced the 5.7 Shurflo Smart Sensor model 5900-0201 pump last week on my coach after 3 yrs of service. Pump started running continuously when turned on & produced less & less pressure. New pump performance is disappointing; it is noticeably noisier with less pressure & with pressure surges. Will be taking the failed pump to Shurflo in Elkhart IN for a failure analysis. I don't buy the over pressure explanation for the cause of pump failures unless the pump is left on while filling the fresh water tank. That may make the pump water hammer and cause a component failure.
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Old 04-04-2008, 01:50 AM   #13
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Dale - Your reasoning for the increased back pressure intrigued me, i.e. the expansion of water when heated. I don't know what size accumulator/expansion tank you have, or if you have none. Assuming you have at least a small one, here are the effects: Water has a fairly linear cooefficient of expansion throughout its liquid state of 207x10-6. So, for a 10 gallon hot water tank, the expansion, in ounces would be, since there are 128 ounces per gallon: 128 oz x 10 gal x .000207 = .26 oz, expansion per degree C. For a typical increase in water temperature of 80 degrees the expansion would be .26 x 80 = 21 oz. If the expansion tank is, say a quart, you wouldn't quite double the pressure if a hot water tank was completely filled with cold water and then heated (maybe go from 20 to 40 psi). Of course, the smaller the expansion/accumulator tank, the greater the effect of water expansion...higher the pressure. Keep in mind also that water tanks usually have air inside them to allow for expansion also, minimizing the pressure increase even more.

Just trying to put something measurable to your theory. Hope you get it sorted out.
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Old 04-05-2008, 12:48 PM   #14
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Last summer we went through several shurflo pumps. After the third replacement I discovered that there's no check valve to prevent the pump from feeding water back into the tank through the tank fill valve if it develops a slow leak. Our pumps were failing because they overheated feeding that small leak. The way I discovered the problem was quite remarkable....I was crawling in the basement one day, when I noticed that water was dripping into the water tank, and since we were not hooked to shore water, it had to be the pump supplying the water. A simple check valve insures that water cannot flow backward from the tank fill valve.
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