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Topic: SHURflo 5.7 pump operating pressure. (Read 6 times) previous topic - next topic
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SHURflo 5.7 pump operating pressure.
Yahoo Message Number: 104075
SHURflo Extreme Series Smart Sensor 5.7 pump.
 Been educating myself about the fresh water system in my LD. Thought I'd share the results of my research.
 In order to better understand the pump, water pressure, water flow, etc., as it applies to my 2008 MB, I called the SHURflo Company.
 On my first call I told the person I spoke to that I was looking for a replacement pump for my RV and was interested in the 5.7 pump. My only concern was a statement in my RV Owners Manual that I should not exceed a pressure of 40 psi in the fresh water system.  I asked if the 5.7 be a good replacement? He quickly and emphatically answered "No, do not use this pump in a 40 psi system. It operates at a much higher pressure". He went on to recommend other SHURflo pumps that would be a good choice for a 40 psi system.
 I then called the SHURflo technical support department. Told the guy I had the 5.7 pump and was curious how it operated, especially as it related to pump pressure. He explained it like this. When you open a water faucet, the pump senses the pressure drop, comes on and pumps water. When you shut the faucet, the pump senses the pressure increase in the water lines and shuts off when the pressure in the water system reaches sixty five (65) psi.  When the pump is not operating, the system remains pressurized to 65 psi until the pump, once again, senses a pressure drop. Hence the statement in the SHURflo Installation & Operating Manual "Pump shut-off pressure is 65 PSI [4.5 Bar]. System must be designed to handle 65 PSI [4.5 Bar]."
 I then asked what a typical operating pressure might be when the pump runs when I have a faucet open. He said there was no way he could answer that question because there are too many variables like the size of the water lines, brand/model of the faucet, etc.  I pressed him for a ballpark and he said probably in the 35 psi to 45 psi range.
 Then I called Vince at Lazy Days and told him I was reading the SHURflo manual and noticed the 65 psi number and I was also aware that my LD Owners Manual contained a comment about not exceeding 40 psi. He assured me they would not have used the 5.7 pump if they thought it posed a risk to the water system. He went on to say *my* system had been pressure tested in excess of 80 psi and the 65 psi cutoff pressure of the 5.7 pump posed no risks.  I want to emphasize the *my* because this information may well not apply to your system. He went on to say that when they were reviewing the Owners Manual, it was decided to leave the 40 psi  city water comment there as a "precautionary statement".  The reality, of course, is that the water system is routinely exposed to 65 psi if you use the 5.7 pump.
 After Victor Sanchez educated me about the relationship between water flow and pressure, I understand the logic of limiting the city water pressure to the 40 psi range as well as the value of the "precautionary statement". For one thing, the standard 40 psi to 50 psi regulator is inexpensive and readily available. Since the high volume 5.7 pump operates in the same general pressure range as the city water regulator and manages to produce a very good water flow, it's clear, as Victor pointed out, that all the restrictions in the city water system are the primary determinant of the water flow and not the pressure. By the time you push the city water through a 25' hose, a pressure regulator, perhaps a water filter and then the water check valve assembly, it's no wonder the water flow I am experiencing is so poor.  I could safely boost the pressure through the regulator to 65 psi if I wanted, but would gain very little, if any, water flow by increasing the pressure past the 40-50 psi range so why bother.  With my Lazy Daze, the best solution to a high water flow rate is to simply run off the 5.7 pump and not bother with the city water connection. That's the plan going forward.
Re: SHURflo 5.7 pump operating pressure.
Reply #2 –
Yahoo Message Number: 104087
Quote
Good info, Ed, and much appreciated! Thanks for passing on those details. :-)

Andy Baird http://www.andybaird.com/travels/
The previous (original) owner of my '07RK had to twice replace the factory installed 5.7 and finally with a 4.0 because the fuse kept blowing, reasons unknown, but the 4.0 works fine with no problems.