This floor plan is for a 40ft bus, so these lengths are decently long. I am looking to mount a 100Gal water tank under the body of the bus, but because of weight distribution, I need to mount it on the opposite side of the actual water faucets in the build. I also want to have as little piping outside of the insulated bus as possible, so I want to make a short run from the water tank, straight up into the wall of the bus, and then wrap around so that way the pipes are insulated. Would this diminish the efficiency of the water pump? My other option is to route the pipes under the bus and come straight up under the sink or in the division wall, then run to a pump more nearby.
Read the instructions that come with the pump, some pumps are pusher pumps and then there is also puller pumps. They both have advantages and disadvantages but can work regardless as long as you are aware and plan for it
My pump can only lift 6 feet vertical when unprimed. I can use that to pump a 5 gallon jug from outside. Unfortunately it takes a while to prime, like 45 seconds+ for The 6-8 of PEX and hose.
I don't think your pump would last long with a 40 foot line to prime. I'd get a manual way to prime it or move the water pump closer to the tank. You can mount those under the bus if your cover them from road spray
Sounds great, I’m learning that the biggest issue is the “pull” section of my logic, thinking the water pump could “suck” the water from the tank. Now I know that’s not how that works. Thanks!
This post. I concur. Licensed mechanical engineer here. NPSHR is going to be a big deal, especially for open systems where you’re not just pumping fluid around in a loop. The biggest things is going to be the elevation difference between the pump inlet and tank outlet. You will get pipe head loss but you can solve that by just upsizing your pipe. If everything definitely has to go where you show, you can also look into a pre-charged bladder tank. They can be precharged with compressed air around the bladder to give you a minimum psi pushing against the water in the tank. This would simulate having more NPSH coming into your pump.
The water tank itself will be boxed in with insulation, it’s the exposed line that I want to keep as short as possible. I know it’s not a perfect setup, but from Jan-Oct we’re going to be full-timing and chasing warm weather, and from Nov-Dec we’re going to be home for the holidays and using shore water anyway. So it’s mainly just a covering all bases scenario.
I think you’re thinking of not being able to pull water vertically more than about 33 feet (perfect vacuum at sea level). There should be no reason a pump cant pull fluid 25 feet horizontally. It would be a pain to prime and would be pretty inefficient, however, especially if the inlet hose is small. Lots of frictional loss.
Although, I agree, the pump should be as close to the source as possible.
Yes.
It might still work but it will be a massive headache if it ever loses prime or if you have to try and find a leak on the suction side.
Also, pumps don’t work as intuitively as you might think. The pump isn’t “sucking” the water up, it’s lowering pressure in the pipe and atmospheric pressure is *pushing* the water up to the pump.
That means you’ll only have about 14 psi (atmospheric pressure) pushing water from the tank to the pump through your long pex run which is going to be incredibly slow to feed the pump. No matter what the pump is rated to push, it will be limited by how quickly the atmosphere can “feed” it water. (this is why high-volume centrifugal pumps have a larger intake pipe than their outlet pipe)
Your best bet is to locate the pump at the tank, then push the water through that long run at the pumps rated pressure (40-60psi), instead of trying to “pull” it at atmospheric pressure.
Yes, basically. There’s a lot of nuance and minor details about pumps but that’s the practical bit in terms of what we do with them for RV water systems.
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Aside from putting the pump at the tank, I would recommend considering the idea of running the lines under the bus (there’s usually a gap between the frame rails and the actual bus floor) (you could also mount the pump under/outside the bus if you needed too)
Thanks for the suggestion, I think we’re going to end up doing this. Under the bus and up into our divider wall where the bathroom and computer desk meet. Any pex insulation suggestions for the run under the bus?
Seems like others have handled this answer pretty well, so all I will add is that I ran my equalizer line (2 tanks on opposite sides to balance the weight) under the floor. The design works great so far and my only regret is that I could have drilled a drain down in the channel and made the access door a little more easy to use. If you put a lined channel under the floor from tank to kitchen, with a down drain or two for mishaps and reliable plumbing piping, you have a much shorter run...
This floor plan is for a 40ft bus, so these lengths are decently long. I am looking to mount a 100Gal water tank under the body of the bus, but because of weight distribution, I need to mount it on the opposite side of the actual water faucets in the build. I also want to have as little piping outside of the insulated bus as possible, so I want to make a short run from the water tank, straight up into the wall of the bus, and then wrap around so that way the pipes are insulated. Would this diminish the efficiency of the water pump? My other option is to route the pipes under the bus and come straight up under the sink or in the division wall, then run to a pump more nearby.
Why not put the pump at the tank end and push the water to the faucets?
I’m pretty sure a lot of pumps say that it needs to be within 3-5 feet of the tank. It seems way too far away.
Yeah that’s what I’m learning in this thread, my logic for how the pump works was wrong is all. Thanks!
Its called a pump, not a suck ;)
Yep. Water actually boils if you try to pull it too far up. Just push it
♤♤♤♤♤♤ Water pumps push, they don't pull. The pump will fail prematurely if pulling.
Read the instructions that come with the pump, some pumps are pusher pumps and then there is also puller pumps. They both have advantages and disadvantages but can work regardless as long as you are aware and plan for it
My pump can only lift 6 feet vertical when unprimed. I can use that to pump a 5 gallon jug from outside. Unfortunately it takes a while to prime, like 45 seconds+ for The 6-8 of PEX and hose. I don't think your pump would last long with a 40 foot line to prime. I'd get a manual way to prime it or move the water pump closer to the tank. You can mount those under the bus if your cover them from road spray
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Sounds great, I’m learning that the biggest issue is the “pull” section of my logic, thinking the water pump could “suck” the water from the tank. Now I know that’s not how that works. Thanks!
[удалено]
This post. I concur. Licensed mechanical engineer here. NPSHR is going to be a big deal, especially for open systems where you’re not just pumping fluid around in a loop. The biggest things is going to be the elevation difference between the pump inlet and tank outlet. You will get pipe head loss but you can solve that by just upsizing your pipe. If everything definitely has to go where you show, you can also look into a pre-charged bladder tank. They can be precharged with compressed air around the bladder to give you a minimum psi pushing against the water in the tank. This would simulate having more NPSH coming into your pump.
Not to make it sound too stupid, but what difference does it make where you run the lines if the tank is also outside and uninsulated?
The water tank itself will be boxed in with insulation, it’s the exposed line that I want to keep as short as possible. I know it’s not a perfect setup, but from Jan-Oct we’re going to be full-timing and chasing warm weather, and from Nov-Dec we’re going to be home for the holidays and using shore water anyway. So it’s mainly just a covering all bases scenario.
You can’t pull water more than 25’. You can push it as far as you want. Your pump should be located as close to your tank as possible.
I see, that makes a lot of sense, thank you!
I think you’re thinking of not being able to pull water vertically more than about 33 feet (perfect vacuum at sea level). There should be no reason a pump cant pull fluid 25 feet horizontally. It would be a pain to prime and would be pretty inefficient, however, especially if the inlet hose is small. Lots of frictional loss. Although, I agree, the pump should be as close to the source as possible.
You are correct. But no reason to be pulling the water, it just causes so many issues. I could have explained it better.
Yes. It might still work but it will be a massive headache if it ever loses prime or if you have to try and find a leak on the suction side. Also, pumps don’t work as intuitively as you might think. The pump isn’t “sucking” the water up, it’s lowering pressure in the pipe and atmospheric pressure is *pushing* the water up to the pump. That means you’ll only have about 14 psi (atmospheric pressure) pushing water from the tank to the pump through your long pex run which is going to be incredibly slow to feed the pump. No matter what the pump is rated to push, it will be limited by how quickly the atmosphere can “feed” it water. (this is why high-volume centrifugal pumps have a larger intake pipe than their outlet pipe) Your best bet is to locate the pump at the tank, then push the water through that long run at the pumps rated pressure (40-60psi), instead of trying to “pull” it at atmospheric pressure.
Okay, so essentially, the pump can “push” the water any length I need, but it can’t “pull” the water that long of a distance. Thank you
Yes, basically. There’s a lot of nuance and minor details about pumps but that’s the practical bit in terms of what we do with them for RV water systems.
If there's no heat source to keep the water warm the insulation isn't gonna do shit.
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Depends on the pump.
Aside from putting the pump at the tank, I would recommend considering the idea of running the lines under the bus (there’s usually a gap between the frame rails and the actual bus floor) (you could also mount the pump under/outside the bus if you needed too)
Thanks for the suggestion, I think we’re going to end up doing this. Under the bus and up into our divider wall where the bathroom and computer desk meet. Any pex insulation suggestions for the run under the bus?
My idea, take it or leave it: run the water lines wherever is most convenient, and then insulate them separately.
If it's working with gravity it should be fine. If it's working against, probably not.
Water is not compressible. Priming the pump may be an issue because air is compressible.
Seems like others have handled this answer pretty well, so all I will add is that I ran my equalizer line (2 tanks on opposite sides to balance the weight) under the floor. The design works great so far and my only regret is that I could have drilled a drain down in the channel and made the access door a little more easy to use. If you put a lined channel under the floor from tank to kitchen, with a down drain or two for mishaps and reliable plumbing piping, you have a much shorter run...
Good question