re-plumbing jetted tub to be self-draining


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Old 08-15-20, 11:39 PM
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re-plumbing jetted tub to be self-draining

Hi folks, I'm in the process of remodeling my bathroom and now have access to underneath my jetted tub. Having read all about bacteria/algae issues related to water not draining from the pipes I had the following questions:
  1. Can I re-plumb the pump so the tub intake is slightly lower than the pump suction inlet? This will drain the intake pipe but will this also cause the pump to have difficulty priming?
  2. How do modern self-draining jetted tubs avoid the pump priming problem?
  3. Similarly can I just raise the flex PVC lines between jets to form humps so pipe water drains out of jets?
  4. Is there a special valve that I can add to the pump piping to allow the air to be bled off while the tub is filling and thereby avoid air-lock?
This is a Kohler model K-1244 bath whirlpool.

Thanks!
 
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Old 08-16-20, 05:45 AM
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Can I re-plumb the pump so the tub intake is slightly lower than the pump suction inlet?
What is a tub inlet and how is it different than the pump suction inlet? Still, you have the tub there in front of you. Look at it and see what you can do.

This will drain the intake pipe but will this also cause the pump to have difficulty priming?
If it is not a self priming pump it could cause trouble. The water level in the tub and whether or not your re-plumbing traps an air bubble in the pump will likely have a bigger affect.

How do modern self-draining jetted tubs avoid the pump priming problem?
The tub is designed so the piping drains but still allows water to get to the pump when the tub is filled to the proper level. They can also use a pump that can self prime.

Similarly can I just raise the flex PVC lines between jets to form humps so pipe water drains out of jets?
That can help but you'll likely have to replumb to have enough slack in the pipes.

Is there a special valve that I can add to the pump piping to allow the air to be bled off while the tub is filling and thereby avoid air-lock?
Yes there are valves that can do that.

All the questions you ask are best answered by you, the person who has the tub right there and can look at it. Your changing the design of the plumbing system so it's up to you to design a system that will work and you've got tight, confined spaces to do it in.
 
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Old 08-16-20, 02:10 PM
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Thanks for your quick reply!

Can I re-plumb the pump so the tub intake is slightly lower than the pump suction inlet?
What is a tub inlet and how is it different than the pump suction inlet?
Sorry for the confusing terminology. I was using the term "tub inlet" to mean the point where the return piping attaches to the tub. I probably should have just said "suction inlet at the tub". By "pump suction inlet" I was referring to the point where the return piping attaches to the pump.

Still, you have the tub there in front of you. Look at it and see what you can do.
Yeah I should have been more precise in my wording. I know it can be physically re-plumbed in the manner I described what I really wanted to know is the ramifications of doing that. I believe you address this below.

This will drain the intake pipe but will this also cause the pump to have difficulty priming?
If it is not a self priming pump it could cause trouble. The water level in the tub and whether or not your re-plumbing traps an air bubble in the pump will likely have a bigger affect.
I have an older model Kohler jetted tub with a 3/4 HP pump model 73524-AA. I plan on calling Kohler during the week but in the meantime do you happen to know if this is a "self priming" pump?

So when thinking about this if I plumb the return line to the pump so it drains the pump intake line when the tub is empty, what is the recommendation on how to ensure air is not trapped when refilling the tub? It would seem to involve getting the slope just right. Is that coreect?

Also even if air gets trapped in the return line to the pump, why doesn't the weight of the rising column of water in the tub, as it is filling, force the air in the return line to squeeze past the gap between the impeller and the pump casing, up the discharge line and out the jets breaking the air-lock?

How do modern self-draining jetted tubs avoid the pump priming problem?
The tub is designed so the piping drains but still allows water to get to the pump when the tub is filled to the proper level. They can also use a pump that can self prime.
So I guess I am looking for design recommendations on how to re-plumb my existing jetted-tub (i.e. how much pump return line slope, etc.) to approach the the self-draining features and minimal pump priming problems that modern jetted-tubs accomplish. So far it seem I need to adjust the pump return line slope and bends in piping between jets. Can you think of anything else?

Similarly can I just raise the flex PVC lines between jets to form humps so pipe water drains out of jets?
That can help but you'll likely have to replumb to have enough slack in the pipes.
Thanks I think that can be done.

Is there a special valve that I can add to the pump piping to allow the air to be bled off while the tub is filling and thereby avoid air-lock?
Yes there are valves that can do that.
I was thinking of plumbing a flexible clear line from the suction inlet at the pump through a simple manual valve then on into the tub over flow pipe. The valve would be easily accessible at the access panel so if I do get an air-lock situation I can bleed the air and any excess water will just spill down the overflow pipe until I shut this priming assist valve back off. What do you think?

All the questions you ask are best answered by you, the person who has the tub right there and can look at it. Your changing the design of the plumbing system so it's up to you to design a system that will work and you've got tight, confined spaces to do it in.
I'm in a unique position where at this stage of the bathroom project all of the tub surround old tile and plywood has been removed so everything is accessible. This will be the only bite of this apple I will get so was looking for some re-plumbing design advice. Not asking for someone to do the engineering for me but just looking for design guidelines, rules of thumb that can be applied in this case or references where I can find such advice.

Thanks!
 
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Old 08-16-20, 02:46 PM
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Personally, I wouldn't spend much effort on this project. If you've ever dealt with this type of plumbing in tight spaces it can be a real knuckle buster to work on. Even with most of the piping draining you'll still have pipes that get filled with dirty water every time the tub is used. Scum will still build up in the plumbing though not as bad as when it doesn't drain. Instead do a monthly cleaning cycle.

To drain obviously everything has to be sloped downhill so the water runs out of the jets and intake when the tub is drained. All the pumps I've seen in jetted tubs are not self priming so you'll want to make sure the pump's impeller is mostly below the waterline when operating the jets. The pressurized jet lines can be run above the waterline so it's easy to put fall in them. I would position your pump so it's intake has a slight downward slope to drain but not so high that the impeller doesn't get covered when the tub is filled to the jets water level. It's OK if the output of the pump goes above the waterline.
 
 

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