Traditional air venturi vs blower for spa

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Brant

Well-known member
Jan 25, 2024
140
Boerne Texas
What are people's opinions on using a traditional passive air venturi set up on their Spas vs a blower to push-inject air. I should have around 15 gpm flow from each jet so I'm not underpowered and dont feel that I need a blower to make up for the lack of jet pressure that many people experience with underpowered spa jets.

Do people tend to prefer traditional venturi setups with the manual air valves on top of the coping or is this not a good option anymore since blowers have become more commonly installed.

What are the cons with either setup? Would I be sacrificing anything by not opting for a blower and using a traditional air valve setup?

Thanks in advance!
 
In reality, the blower does not really add much in the way of strength to the jets because it is just air. The main purpose of a blower is to clear the air line of water when the jets are first turned on. However, not every spa design can work without a blower. Most PBs do not understand hydraulics and spa jet design very well so that is why they use the blower.

Also, you do not need to have the passive lines control at the spa. You can still remote the air line to the equipment pad if you want it that way but only if the PB installs a Hartford loop near the spa.

If you are in the design phase, you need to make sure the PB is designing the spa properly.

- Use a dedicated pump for the spa jets. No heater or filter in line.
- Use large enough pipe for the number of jets and the jets size.
- Do not use too many jets for the pump size, jet size and plumbing design.
- If you are remoting the air line, make sure the air line is at least 2.5" and has a hartford loop near the spa wall

But how do you know you will actually get 15 GPM/jet? Has anyone done the calculations?
 
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mas985 said:
In reality, the blower does not really add much in the way of strength to the jets because it is just air. The main purpose of a blower is to clear the air line of water when the jets are first turned on. However, not every spa design can work without a blower. Most PBs do not understand hydraulics and spa jet design very well so that is why they use the blower.

Also, you do not need to have the passive lines control at the spa. You can still remote the air line to the equipment pad if you want it that way but only if the PB installs a Hartford loop near the spa.

If you are in the design phase, you need to make sure the PB is designing the spa properly.

- Use a dedicated pump for the spa jets. No heater or filter in line.
- Use large enough pipe for the number of jets and the jets size.
- Do not use too many jets for the pump size, jet size and plumbing design.
- If you are remoting the air line, make sure the air line is at least 2.5" and has a hartford loop near the spa wall

But how do you know you will actually get 15 GPM/jet? Has anyone done the calculations?
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I understand the Hartford loop and hydraulics (within reason).

I like the idea of passive air line control for the ability to turn air injection on/off at will. I know my wife will not want to have air on all the time when she is in the spa. With a blower and check valve, I've seen that when the blower is off, it doesn't allow sufficient air into the system to inject into the jets. If I dont have the ability to control/limit/stop air from coming it, the jets would be air injecting all the time and this is not desirable for us. So I need air control or a blower setup.

I've sat in uder-powered Spas that had to have the air blower on to feel anything from the jets. I didn't want this so I'm doing a separate 3hp variable speed pump on an independent circuit that will supply the jets only. I'm running 3" piping to and from the pump, my pump is flooded and the lines are short runs. I shouldn't have any issue getting 130 gpm or more output from this setup. I planned on 8 jets so yeah, 15 gpm should be an easy target to hit.
 
I'm leaning towards air control knobs on the coping rather than an all or nothing blower setup. I don't like the look of knobs but I like the ability to control how much air is allowed into the jets. I'll probably split the jets into 2 groups with 1 air controller each. Can 1 air controller feed 4 jets or do I need to have more air contollers?
 
Brant said:
I like the idea of passive air line control for the ability to turn air injection on/off at will. I know my wife will not want to have air on all the time when she is in the spa. With a blower and check valve, I've seen that when the blower is off, it doesn't allow sufficient air into the system to inject into the jets. If I dont have the ability to control/limit/stop air from coming it, the jets would be air injecting all the time and this is not desirable for us. So I need air control or a blower setup.
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Venturi tees are used with or without a blower so turning off the blower does not necessarily turn off the air to the venturis. They will still try to suck in air and blowers will allow some air to get through even when they are off. You may also need a valve to shut off the air so that may not be a great solution.

Brant said:
I've sat in uder-powered Spas that had to have the air blower on to feel anything from the jets. I didn't want this so I'm doing a separate 3hp variable speed pump on an independent circuit that will supply the jets only. I'm running 3" piping to and from the pump, my pump is flooded and the lines are short runs. I shouldn't have any issue getting 130 gpm or more output from this setup. I planned on 8 jets so yeah, 15 gpm should be an easy target to hit.
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What pump are you planning for? An Intelliflo 3 with 65' 3" lines will barely make 16 GPM per jet. Personally, for 3/8" jets, I would target 19 GPM so when you want, you can have really strong jets.
 
Brant said:
I'm leaning towards air control knobs on the coping rather than an all or nothing blower setup. I don't like the look of knobs but I like the ability to control how much air is allowed into the jets. I'll probably split the jets into 2 groups with 1 air controller each. Can 1 air controller feed 4 jets or do I need to have more air contollers?
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The only ones I have seen for spa side are the small diameter that sit right above each of the venturi jets. That way it gives you control on a jet by jet basis.
 
mas985 said:
Venturi tees are used with or without a blower so turning off the blower does not necessarily turn off the air to the venturis. They will still try to suck in air and blowers will allow some air to get through even when they are off. You may also need a valve to shut off the air so that may not be a great solution.


What pump are you planning for? An Intelliflo 3 with 65' 3" lines will barely make 16 GPM per jet. Personally, for 3/8" jets, I would target 19 GPM so when you want, you can have really strong jets.
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Yeah, intelliflo 3 VS with around 30 ft lines. I'm not using a bigger pump or lines. I'll get what I get out of this setup and be happy enough.

I don't want a knob for each and every jet. That would look awful. I'll probably be contacting CMP or waterway to find out what they recommend. I would consider up to 4 knobs but that is even on the higher end of what I'm willing to do.

I don't see why one knob wouldn't be able to supply 3 or 4 jets, it's my understanding that the multi-jet gunite bodies only have one air inlet. I would assume that they would be able to be fed from one air controller. As such I would assume they make air controllers that have larger orifices??? I guess I'll probably need to reach out to the people who design the equipment.
 
I had assumed you were using individual jets like this:


1713556411823.png

OR are you using jet manifolds like this:

1713556434573.png

This clusters 3 jets for an individual.

But how are you calculating the flow per jet? The above would require 45 GPM (3x15), not 15 GPM.
 
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i was using a multi jet body it as an example to the air question. i dont know what gunite housing(s) im using yet because i haven't finalized what i want to do. i may use singles, doubles, triples or whatever. i'm not set on any specific set-up yet. i just know that im planning on around 8 jets total. since the gpm needs are based on orifice size, if i decided to do a triple, i could reduce the orifice size to match available flow.
 

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Brant said:
i was using a multi jet body it as an example to the air question. i dont know what gunite housing(s) im using yet because i haven't finalized what i want to do. i may use singles, doubles, triples or whatever. i'm not set on any specific set-up yet. i just know that im planning on around 8 jets total. since the gpm needs are based on orifice size, if i decided to do a triple, i could reduce the orifice size to match available flow.
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When you reduce the orifice size, the required flow rate is reduced as well to maintain the venturi effect. However, the strength and/or force of the jet is proportional to the product of the flow rate and orifice velocity (i.e. fluid momentum). A 3/8" jet at 15 GPM would have an impact force of around 1.4 lbf. A 5/16" jet at 10 GPM would have an impact force of 0.9 lbf or a force reduction of about 1/3rd. But if you have a cluster of 3 so total force for each person works out to be more for the 5/16". However, the number of clusters would be limited by the pump capability to around 4 clusters of 3 5/16" (12x10=120 GPM) vs 8 of the individual 3/8" (8x15=120 GPM). All trade offs.

Brant said:
but as you can see, the 3 jet body has 1 air inlet. i assume someone makes an air control knob that is big enough to work with this body.
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Yes, with the cluster it makes sense to have a single air inlet. However, one thing to consider, a single jet typically needs a 3/4" air line and the 3 jet cluster I showed above requires a 1.5" line. The valve and fitting setup would be pretty large for something like that. If the air line is smaller than it should be, it will be louder as well due to the higher air velocity. Air vents near the spa are loud enough without undersizing them.
 
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mas985 said:
When you reduce the orifice size, the required flow rate is reduced as well to maintain the venturi effect. However, the strength and/or force of the jet is proportional to the product of the flow rate and orifice velocity (i.e. fluid momentum). A 3/8" jet at 15 GPM would have an impact force of around 1.4 lbf. A 5/16" jet at 10 GPM would have an impact force of 0.9 lbf or a force reduction of about 1/3rd. But if you have a cluster of 3 so total force for each person works out to be more for the 5/16". However, the number of clusters would be limited by the pump capability to around 4 clusters of 3 5/16" (12x10=120 GPM) vs 8 of the individual 3/8" (8x15=120 GPM). All trade offs.


Yes, with the cluster it makes sense to have a single air inlet. However, one thing to consider, a single jet typically needs a 3/4" air line and the 3 jet cluster I showed above requires a 1.5" line. The valve and fitting setup would be pretty large for something like that. If the air line is smaller than it should be, it will be louder as well due to the higher air velocity. Air vents near the spa are loud enough without undersizing them.
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Good info. Thanks. Maybe a blower is what we do. Maybe add an open to atmosphere valve by the blower so I can use it without the blower running. Just let the line suck as much air as I allow it
 
Again, you don't actually need a blower if the air line is designed properly and the flow rate to the jets is sufficient. I have a 6 jet spa with 15 GPM jets and no blower. I get more than enough air for the bubbles without a blower. Adding a blower would just put a lot of water on the deck without increasing the strength of the jets.
 
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mas985 said:
Again, you don't actually need a blower if the air line is designed properly and the flow rate to the jets is sufficient. I have a 6 jet spa with 15 GPM jets and no blower. I get more than enough air for the bubbles without a blower. Adding a blower would just put a lot of water on the deck without increasing the strength of the jets.
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Sure, i can plumb it as such and just add a blower later if I feel the need.

How do you prevent bugs from crawling into the air line and making a home? Do u have a screen/air filter on it?
 
I have a grate across the end of the pipe. That prevents critters from getting in and plugging the pipe. Not so worried about the smaller stuff. I never noticed anything coming out of the jets so I just assumed they have no interest or too small to notice.
 
AQUA~HOLICS said:
Two separate sets of jets in the spa.
First set runs off a XF Pentair pump with 8 jets (This is the main pool pump).
Second set runs off of a standard VS pump with 6 jets.
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What you said about two pumps got me thinking. I have one 3hp pump that was going to run jets only. The pool's 3hp pump (when in spa mode) was only going to return hot water to the spa. Now that I think of it, why not plumb the pool (heater) pump into the same jet loop with the dedicated jet pump? This should increase my output to the jets significantly. I could probably get 200 gpm through the system and easily power 10 jets (maybe more). I understand that plumbing size plays an important role but if I have a double 2" loop in the spa feeding the jets with both pumps connected, it would be a lot more powerful than with just the 1 dedicated jet pump. I was already running a return line to the spa for my overflow and for hot water. The plumbing wouldn't change much other than increasing it from 2" to 2.5".

Thoughts?
 
A typical pool/spa system that I advise customers to consider is a XF Pentair pump for the main pool pump (80 more GPM plumbed with 2 1/2 “ pipe) that will run up to 8 jets in the spa alone. Then a second pump VS Pentair for an additional 6-8 jets (plumbed with 3” pipes).
When the homeowners are using the spa alone (2-people) the main pool pump is in service running 8 jets plumbed through the heater, when more people are in the spa the dedicated spa booster pump is activated to run the other jets that only recirculate the heated spa water.
Have not personally seen a system that runs the spa booster pump through the heater along with the pool/spa pump.
 

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