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Old 05-17-2017, 11:59 AM   #1
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Pump placement

So I'm getting around to installing my water system and I'm having a brain fart. The correct sequence is Water tank ---> water pump ---> T split ---> one goes to hot water heater then to sink/shower hot, other side goes to sink/shower cold

Is that correct? That way both sides have pressure from the pump. I was then going to install a switch under the sink so that I could flip it, turn the pump on, and have hot/cold water. Don't want to mess this up and definitely not a plumber.
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Old 05-17-2017, 12:19 PM   #2
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That'll work with a conventional rv water heater. If you use an on demand water heater you should use separate pumps as most on demand heaters have both flow and pressure requirements that a single pump probably won't handle.

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Old 05-17-2017, 12:53 PM   #3
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That'll work with a conventional rv water heater. If you use an on demand water heater you should use separate pumps as most on demand heaters have both flow and pressure requirements that a single pump probably won't handle.

Jack
I was looking at on demand. I can't use a heavy duty Shur-Flo pump?
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Old 05-17-2017, 02:31 PM   #4
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Check the requirements on which ever heater you are looking at and make your pump selection accordingly. Error on the side of higher flow rate and pressure under full flow. Too little pressure or flow if even a bit will cause your heater to cycle on and off resulting in occasional bursts of cold shower water---burrrrrr. Definitely plan on two pumps if you go with the on demand heater. Both can be operated by a single switch and will operate without regard to each other.

I use an on demand heater in my bus which has a recirculating circuit on the hot side so never a lack of hot water.

Jack
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Old 05-17-2017, 03:24 PM   #5
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Most tankless water heaters have a 1/2gpm flow sensor.
(will not fire with less than 1/2gpm flow)

One pump is adequate. No need for more than 1. Just make sure you can get more than 1/2gpm when factoring in the pressure drop of the pipe size and length (and any other potential flow restrictions you build into the plumbing system)

I'm not a bus expert, but if you have plumbing questions, fire away!
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Old 05-17-2017, 05:26 PM   #6
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The cheapest of the demand heaters (for example, Eccotemp) use a pressure switch rather than a flow sensor. Those are the heaters most likely to need dual pumps in order to develop enough pressure to reliably keep the unit fired. I have the Eccotemp L5 and have done a few experiments with it. I don't think a person would be happy with the result if they tried to mix hot and cold water to get the shower "just right" -- that heater seems to be designed so that one adjusts the flow knob until the flow is low enough (pressure is high enough) to keep the burner lit, then adjust the gas knob to get the temperature right. Running cold water elsewhere could upset the balance of the flow knob and cause the unit to extinguish due to low water pressure... which can be "fixed" by the addition of a second pump as ol trunt suggests, or by using a better heater with a flow switch instead of a pressure switch.
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Old 05-17-2017, 06:47 PM   #7
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If your going to have a hookup for city /park water I would put a check valve just after the pump.
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Old 05-17-2017, 08:26 PM   #8
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S&F. That would be a good idea--it would prevent any chance of city water passing backwards through the pump and over filling the water tank.

CC and FW, I use the Ecotemp L5 and I can assure you that it requires both an adequate flow rate and adequate water pressure per the owners manual and personal experience.

Until I solved those problems the Ecotemp was on my s#@t list. Though I can't provide the specific pump model Ecotemp recommends without opening my water heater cabinet (lots of screws), it can be easily found on one of the Ecotemp websites.

As to two pumps, for the $50 they cost, why would anyone risk the failure of a single pump while dry camping miles from nowhere? I don't see anything sporting about trying to get my next drink from the run off in the rain gutter.

Jack
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Old 05-17-2017, 08:51 PM   #9
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I'm not trying to cheap it, but K-I-S-S. I saw the higher end Shur-Flo's have 3gpm. I have the Ecotemp L10. Neither of these products are cheap. If two pumps is the way to go I'll do that. I have no city hookups. My bus is fully off grid. I was worried more about power requirements but even 5 amps each for the duration of a shower is not going to put a dent in my battery bank.
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Old 05-17-2017, 11:32 PM   #10
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Quote:
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S&F.
As to two pumps, for the $50 they cost, why would anyone risk the failure of a single pump while dry camping miles from nowhere? I don't see anything sporting about trying to get my next drink from the run off in the rain gutter.

Jack
Like Jack, I have two pumps, in my case the good ol' Shurflo 2088 that are simple and work well, and are probably still the most reliable pump out there. I mounted each one on an easily-removable shock-absorbing mount and use quick-connects for the water lines and power wires - this way it takes less than a minute with no tools to completely remove a pump for any servicing or PM. Pumps are cheap enough that it's silly to not have a spare or back-up pump connected and ready for immediate use. To make it easier to diagnose problems, I have two 100 PSI gauges, one for incoming city water pressure and the other for in-bus water pressure; I set each pump's internal regulator to 40 PSI, the same as the Watts adjustable brass regulator, then I always have 40 PSI whether I'm on tank or city water.

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