Let's talk water pumps!

[Johnny M]

Let's talk water pumps! First here is my water setup for my Boler's custom wet bath:
~16 gallon on board fresh water tank
~Seaflo 1.2 GPM 35 psi water pump 12vdc
~1 sink faucet with pull out sprayer for the shower head
~Fastair tankless propane water heater
~1/2" CPVC cold and hot water lines
~2 CPVC valves to control city or tank water

First, the water system works on both city water or tank water as intended with two exceptions.

First, when I am on tank water the pressure is usable but weaker than I desire. The volume of 1.2 gallons per minute is ideal as it allows for conservative use of our tank water.

Second is water temperature control; with the propane tankless water heater it heats up more when briefly turned off (could burn you if not careful) and takes a few seconds to get up to temperature which can waste water. For the most part it works better on city water hookups but you still must be cautions for any hot water in the line when turning on.

My goal is to modify my pump or replace it all together so I can have the same 1.2 GPM flow but significantly increase pressure when on tank water. Pump is not used when on city water, system relies on water system pressure.

I would also like to improve on the regulation of water temperature regardless of the use of tank water or city water. I have noticed that when on tank water the tankless water heater will shut off if I set the min/max water flow control on the water heater to half or more, and comes on when set to anything less than halfway. The flame control also has min/max settings so between the two you can set it to the desired temperature. It is easier to set on city water with good pressure, but can still be difficult to set to an exact degree in temperature such as 39 degrees celcius. It is more difficult to set on tank water as I am limited to half of the heaters maximum water flow due to either low psi, low GPM or both.

I have given considerable thought to a small mixing tank to temper hotter water temperature but it would involve a more complicated water system and at least 1 additional pump plus sensors and electronic controls beyond what I see as feasible for our small camper.

Anyone have any engineering input or ideas on a simple solution to address both issues?

[Civilguy]

John,

Here's a few quick thoughts. My limited experience with an electric tankless heater feeding a lavatory sink long ago was that it tended to constantly cycle on and off and produce untempered flow, first too hot, then briefly cooler as it cycled. It was enough to leave a bad impression ever since.

It sounds like the newer heater you have (rated 2 gpm?) is supposed to give you the ability to tune it's behavior with the two controls. I suspect that would work best if the draw was always the same, meaning to one faucet only, or two different fixtures at the same "distance" from the water heater.

The distance could perhaps be made the same by adding some pipe to the shorter run. Then you might be able to balance the two controls on the heater to try and obtain a consistent performance.

Ultimately, I think this style heater will work best running a long constant draw while balanced, which unfortunately then causes too much water use when boondocking or using holding tanks.

A small inline tank or short length of large-diameter pipe could moderate the temperature swings a bit, but in turn it could potentially result in more wasted water when the cool water in the tank needed to be flushed out during a subsequent draw to obtain more hot water after the contents of the tank had cooled.

There are mechanical mixing valves available which will control the temperature by mixing hot and cold water. This might be your best bet.

I have seen a trailer where the owner used a smaller diameter (1/4"?) poly line for the hot water supply to the fixtures in order to reduce the water which was wasted when drawing hot water. However, this was used on a trailer with a tank-style water heater. The smaller diameter line would tend to carry any temperature cycling to the faucet with no tempering.

I'm not clear why you'd need a second pump. As to increasing pressure, then there are some factors which come in to play which will tend to increase the flowrate. A positive displacement pump can provide higher pressure at lower flow rates, but that might be getting a little exotic; translated, a little exotic may mean very expensive.

I will try to look at this again and see if I provide any better information in the morning.

[Johnny M]

I only have 1 fixture for a small sink in the wet bath and the faucet pulls out and extends as a sprayer which doubles as a shower head. I need to confirm the specs but I believe it is a 2 gallon/min unit for the Fastar water heater. The thought of the 2nd pump was over thought - one to pump from tank to WH then to a mix tank to temper, a second pump to draw from the temper tank to the faucet, probably not necessary. I had in my head some temperature sensors and electronic valves to regulate a specific temperature automatically. Ideally with a thermostat. With the Fastar unit you are the thermostat but it does provide a digital temperature readout in celcius. Controls are a little finiky in the setup but once it is set I don't have to mess with it until we change water source. A better control for both flame and flow regulation for very small adjustments would be an improvement. Simple fix may just be a pump with higher psi but same gpm. Gonna give it some more thought and sleep on it.

[Borrego Dave]

Originally Posted by Johnny M

I only have 1 fixture for a small sink in the wet bath and the faucet pulls out and extends as a sprayer which doubles as a shower head. I need to confirm the specs but I believe it is a 2 gallon/min unit for the Fastar water heater. The thought of the 2nd pump was over thought - one to pump from tank to WH then to a mix tank to temper, a second pump to draw from the temper tank to the faucet, probably not necessary. I had in my head some temperature sensors and electronic valves to regulate a specific temperature automatically. Ideally with a thermostat. With the Fastar unit you are the thermostat but it does provide a digital temperature readout in celcius. Controls are a little finiky in the setup but once it is set I don't have to mess with it until we change water source. A better control for both flame and flow regulation for very small adjustments would be an improvement. Simple fix may just be a pump with higher psi but same gpm. Gonna give it some more thought and sleep on it.

John, I have no hands on experience with a tank less system other than comments from some that had them in their homes. I do believe all said the first water temps were high before leveling off. As far as your GPM, you may want to look into possibly what you could change with flow restrictions in the faucet head. I've drilled out the holes to the next size larger before and it really helped . On one old RV I had when the 35PSI pump was starting to give up the ghost I replaced it with a 45PSI Sureflow pump, big difference.

[J Ron]

Johnny M. Pressure is what produces flow. If you want higher pressure, higher flow comes along with it. I find that a certain amount of water is needed to do any particular job regardless of flow. If a quarter of a gal is needed to do a job, such as wetting down in the shower, higher flow just does the job quicker. The big thing is how many jobs is needed to be done and is there enough water capacity to do those jobs. Real key to using less water is doing less jobs that need water.

[Civilguy]

Originally Posted by Johnny M

I only have 1 fixture for a small sink in the wet bath and the faucet pulls out and extends as a sprayer which doubles as a shower head. I need to confirm the specs but I believe it is a 2 gallon/min unit for the Fastar water heater. The thought of the 2nd pump was over thought - one to pump from tank to WH then to a mix tank to temper, a second pump to draw from the temper tank to the faucet, probably not necessary. I had in my head some temperature sensors and electronic valves to regulate a specific temperature automatically. Ideally with a thermostat. With the Fastar unit you are the thermostat but it does provide a digital temperature readout in celcius. Controls are a little finiky in the setup but once it is set I don't have to mess with it until we change water source. A better control for both flame and flow regulation for very small adjustments would be an improvement. Simple fix may just be a pump with higher psi but same gpm. Gonna give it some more thought and sleep on it.

Well John, the fact that you only have one faucet simplifies things. My experience has primarily been with larger pumps and with low-flow chemical feed systems, so, I can't always be real specific about RV systems and equipment. But I can speak to some of the principles involved. A friend once rightfully observed that if someone asks me what time it is, my tendency is to explain how to build your own clock. That's sadly true. But, maybe this will be of use and/or interest.

Your pump draws from the on-board fresh water storage tank and feeds both the water heater and the cold supply piping. As you say, there's no need to change that. If your pump is cycling off and on, and this is impacting the temperature delivered at the faucet, you could add a small pressure tank (accumulator) located on the discharge side of the pump and the intake side of the water heater. That would reduce the pump cycling and might make it easier for the water heater to regulate temperature under a more constant flow condition.

Thermostats have what we call a dead-band or hysteresis. That's the temperature range between when the heat source is turned on or off; like 'on' at X degrees and 'off' at X+10 degrees. That would be a ten-degree dead-band. A narrow dead-band will cause rapid cycling of the heater. You likely have no control over the dead-band. So, your best bet is to tune the heater to the "normal" flow rate as best you can.

I disassembled the pump on our Casita. (Flojet 3526-144, 12VDC fixed speed, 5.2 A, 50 psi max) so I have some idea how that one works. It's basically what I would call a positive displacement pump. This means that the flow won't vary much under different pressures and you can get the higher pressure you are looking for. So far, so good.

I am not clear how the variable speed pumps marketed for RVs are set up, so I can't advise you on whether a variable speed pump might be a good option to smooth out the flow and temperatures.

As far as controlling temperature goes, my limited experience is with specifying very expensive units to temper water for eye-washes in chemical-handling areas. More recently, the codes have changed to require that showers in homes have a temperature control valve to reduce scalding incidents. That change has brought these temperature mixing valves (TMVs) from the realm of the crazy-expensive into the realm of just-plain-expensive, or perhaps even affordable.

These are mechanical devices; they don't require any wiring or control system. They have two inputs (hot and cold) and one output (blended). You would plumb one so that the mixing valve would supply the "hot" side of the faucet while the cold connection is supplied from the trailer's cold water piping as it normally is. Please refer to the diagram I posted below.

Here's links to a couple of TMVs that popped up on Google. I think you would want the smallest size, 1/2" inch. However, it would be good to talk to a vendor and/or read up on these and verify the suitability for your application.

In-Line Thermostatic Mixing Valve [MixingValveCRP-075] | DudaDiesel Biodiesel Supplies

Thermostatic Mixing Valve - Webstone Valve Innovation

[Mike_L]

I've never been a big fan of the tankless water heaters in trailers because of the difficulty with temperature fluctuations. A low flow shower head uses less water and a 12 volt RV pump is better able to maintain pressure with a low flow head. I use a shower head with an on/off switch so I only have to balance the hot and cold flows once.

[Joe Romas]

No first hand experience but we live in an older community that has low water pressure.
Several on our block have tried tank-less heaters and have had unsolvable problems that were traced back to low pressure/flow.

Do you have an accumulator in your trailer?
It might help by regulating the pressure to a even amount.

Joe

[Johnny M]

Thanks guys for all you post, especially Civilguy, very detailed and informative! I called Seaflo on Friday and explained the problem I was having and after he explained how to adjust the allen head screw on the pressure switch I realized there wasn't one. Apparently the pump I bought a couple years ago was an old style right about the time Seaflo usa was formed. So what I got was one of the old style from the overseas Seaflo company. The new usa based company designed a new pressure switch, so the guy I talked to is sending me one to replace on my pump after saying he would honor their 4 year standard warranty even though mine was made before Seaflo usa came about. That impressed me.

As a retired firefighter I am familiar with pressure, flow, volume, friction loss and a number of other factors regarding pumping water but all of it pertains to firefighting apparatus, so these small volumes and water pressures in rv water systems are a quite different even if the general principles are the same.

What I did discover was that the cheap looking plastic shower head that came with the water heater is obviously a low flow high pressure shower head as when I switched out the expensive laundry sink faucet/sprayer combo for the shower head I had a good amount of pressure to shower with. With the laundry faucet in place, there wasn't enough pressure using the Seaflo pump to make the spray feature kick in beyond a strong trickle/partial weak spray, but using it as a regular faucet stream was fine for hand washing. And the 16 gallon tank emptied in about 16 minutes give or take (about a gallon a minute). But with the shower head that came with the water heater, the spray was good and strong enough for a suitable shower including hair washing when boondocking. I also discovered that the tank water will last twice as long or more as at 15 minutes of constant flow my tank was less than half empty. With an on/off switch on the shower head I could likely get 2 to 3 days out of a tank by way of a navy shower. The water heater shower head also made it easier to regulate the temperature to around 39 degrees Celsius.

I have thought about adding an accumulator tank to see how the system performs with the pump and water heater combo and I may do so soon as I have plenty of room for one. For right now I am going to see if I can find a similar but better quality low flow high pressure shower head as the plastic one has a small crack in it.

All in all, I like boondocking in the National Park primitive campgrounds as well as the Nation Forest Service Campgrounds. One reason being they are cheap compared to commercial campgrounds and even state parks here in Georgia, so its and excellent way to spend a weekend or a week without breaking the bank, but more importantly I like the more remote feel and the peace and quite that goes along with that style of camping, like next to the mountain stream or overlooking the valley below. Now my wife she is more of a RV resort type, but as long as she has a hot shower and a toilet she is coming around to the idea of the peacefulness of the boondocking experience.

[redbarron55]

As a Fastar userI understand where you are coming from.
You have the winter/summer setting and the winter is hotter and the summer is cooler.
It does take a little fiddling with to get the temp where you want it.
I also installed an accumulator so the pump does not cycle on an off as much.
We have made a wet bath in the front of out 16' Scamp with a shower head with a shutoff.
We do not generally mix the cold and hot, but rather set the summer temp for showering and then the winter setting for washing dished etc.
It does take a short while to get up to temp, but it has worked for us.
I have thought about using a circulating pump and a small tank with a radiator for a little cabin heat and you could tap off this for warm water that has better regulation.
If you circulate from the tank through the tankless heater it will heat the water when is gets cooler, but then you might as well install a regular water heater.
Any solution is by definition a compromise in some area, money, space, weight complication etc.
Our Fastar meets out needs but can be fussy. Luckily we are not.
I use an adjustable pump from Baron Marine which is a cheap Chinese knockoff of something and the switch did need adjusting. The accumulator helps and my system is set up with the pump from the tank to a check valve and tee to city water.
My problem right now is replacing the pump I have for the shower drain pan as I used an old Seaflow that has locked up and popped the fuse on our trip this last weekend.
I have a diaphragm with a motor and belt and this one I think I may put in the bottom of my closet to keep it dry and clean.
As to your problems I think that higher pressure and flow will make it manageable and the accumulator will probably help.
By the way for those who consider using the tankless like we have is if you blend the cold and hot and are on the edge of the flow start point for the heat turning on it will really cool off when the heater quits firing!.
This is why I set the heater for the warm water temp I want without blending with cold.
So far for the money I have in the Fastar and the internal space not used in the camper I an satisfied.

[Johnny M]

I agree JD that it is a compromise somewhere. I made lots of those during the re-design of our Boler's interior. And yes I did also find it to be true that if you open the cold water valve too much that it takes away from the hot water pressure flowing through the water heater and will cause the w/h to shut off until you close down the cold. This was more of an issue with using tank water and not as much of an issue with city water hookup but that depends to on the city water pressure.

I still had issues with the shower/sink drain but I have improved it by adding an exterior vent pipe (doubles as a flag pole) that connects in between my plumbing drain connection and the hose leading to the portable gray tank or sewer connection. It seemed to be getting a vapor lock between the gray tank and the shower and sink. I tried a very short vent pipe this past weekend but it didn't work well so I am going back to the tall one but I will just cut it in half and add a PVC connector in the middle so as to be able to store it more compactly when in tow.

As for now I am hunting for the right shower head to replace my low flow plastic one that has a crack in it and I may add a separate fixture for the shower head and just go with a regular faucet for the sink.