Water backing up into Venturi

[Phantom Of Utopia]

We moved into our house 3 years ago. Our house has a 17 year old pool in good working order, which includes an attached 4 person spa,
also in good working order. This is the first time I've lived in a house with a pool. We moved in at the end of the season. Before the next
season we hired a company to drain the pool, steam clean it, and (after we filled it) open it. The spa worked fine.

At the end of our first full season we had the same company (which I'll call "company A") close the pool for us. The company removed all the
jets from the pool and put plugs in. They blew the lines clear of water, obviously to prevent damage during the winter. Here in New Mexico
we do get some fairly cold snaps.

The next season they came to open the pool, but it turned out they had damaged some of the spa jets. These were jets with ball bearings inside
of them. I tried to replace them with a similar part (218-6010). Oddly, the spa had three different types of jets in them: two of the ball
bearing jets, and two with no moving parts. Although I managed to order two of the damaged ball bearing jets,
I see at hotTubParts.com that they are no longer offered.
This seems to be a similar part: Poly Internal Std Roto Deluxe: Hot Tub Parts for Spas - Quality Spa Parts Company . After they opened the pool the spa jets would not aerate.

Company A came by to fix the spa, but were not able to get it to work. With all the jets in place the water was backing up into the air inlet,
(which I understand is called the venturi) and spilling out. They announced they couldn't fix it but suggested I consider
attaching a high-volume compressor to the venturi. I hired a second company (company B) to have a look, they announced
that the problem was that the spa had check valves buried in the concrete that could only be replaced by tearing apart the concrete. A third
company (company C) came by and said they thought the problem was that the jets were restricting the water too much, but they didn't know where to
order less restrictive jets.

Given that the spa was working before company A closed the pool, I didn't think a compressor was necessary. Aside from other considerations
it will require running an expensive electrical line out by the pool. Company B's suggestion seemed ludicrous. I was not able to find anything
like a check valve, and it seems daft to me that someone would build anything that required a check valve in such a manner that it would
require tearing through a foot or more of concrete to replace it. After much online research I was unable to find any references to internal
check valves.

I ordered a set of adjustable jets. I bought 4 of these(Hot Tub Parts for Spas - Quality Spa Parts Company)
and installed them with the orifices removed, to allow for maximum water flow. Unfortunately, even without the orifices, water backed up into
the venturi and began overflowing. (They have no moving parts)

I did try installing just the 2 ball bearing jets I have and partially covering an inlet pipe with my hand. I saw no aeration, and water started
backing up into the venturi.

As near as I can tell there is nothing in the lines. There seems to be plenty of pressure.

Does anyone have any ideas on how I can fix this?

 

[Poolbreh]

Can you give pics of new jets, old jets, pics of inside with jets removed and placement of your air intake?

 

[1poolman1]

If you cover a jet it will force water back up thru the air line. A broken or clogged jet will do the same.

 

[Poolbreh]

You can also remove the new jets and see if you have the backup up problem. You can also remove all the jets and see if it’s more of a jet head problem or internal.

 

[Phantom Of Utopia]

If I remove all the jets I have no backup problem.
Pictures of the adjustable jets are here:
Hot Tub Parts for Spas - Quality Spa Parts Company
Four of these (one in each pipe exhausting water into the spa) provided enough back up pressure to send water into the Venturi.

The jets with the ball bearings look like this: Hot Tub Parts for Spas - Quality Spa Parts Company

Here are pictures of the spa, and the Venturi. It is normally covered, and appears to me to just be a thick 1.5 inch poly pipe.

 

[Poolbreh]

Here are pictures of the spa, and the Venturi. It is normally covered, and appears to me to just be a thick 1.5 inch poly pipe.

Covered with what? Where is the air intake located? Ah last pic just popped up.

 

[1poolman1]

The venturi are in the jets themselves. What you have labeled as that is just the air supply line, 1.5" PVC. Removing the orifices from a jet will allow it to flood the air line and cause what you are seeing.

 

[Poolbreh]

It looks like they cut out the air intake valve to blow the line. Was it always just open like that?

 

[Phantom Of Utopia]

Oh. My vocabulary is wrong. Sorry, I'm a noob.
Okay, this is NOT what I would have expected. I thought that as the jet orifice size decreased, the air line would back up more and more because it is adding back pressure.

Poolbreh ... are you saying there might be some sort of valve that fit inside the air pipe? I'll have a look but I don't think I have anything like that ... what would it be called, perhaps I could order a new one?

 

[Poolbreh]

Your setup is not what I usually see, it looks like it’s designed very similar to an above ground spa. Since your air intake is so close to the spa and low I would imagine some type of air intake valve or cap that reduces backup, having it open like that can’t be right. Since you said it happened after winterizing I’m guessing they cut it out to blow the lines. Maybe @1poolman1 knows or @RDspaguy.

 

[Phantom Of Utopia]

Your setup is not what I usually see, it looks like it’s designed very similar to an above ground spa. Since your air intake is so close to the spa and low I would imagine some type of air intake valve or cap that reduces backup, having it open like that can’t be right. Since you said it happened after winterizing I’m guessing they cut it out to blow the lines. Maybe @1poolman1 knows or @RDspaguy.

The pipe is pretty much cut at the same level as the concrete. It's a sloppy cut, to be sure, but the top of the pipe is very close to the cover (which I removed to take the pictures). So if there is a valve, it must sit INSIDE the pipe. I don't recall ever seeing a valve ... but it is possible I just didn't look. I certainly don't have one now. Could the bloke who closed the pool removed it and absentlmindedly tossed it into his tool box? Sure. I don't think he was dishonest, but he was somewhat absent minded.
If I was to replace the valve I'd need to know what it was called to be able to search for it online. Do you know the name?

 

[Poolbreh]

We have to wait for people smarter than me. I don’t want you ordering something you don’t need.

 

[1poolman1]

Something like this would have normally been in an air line that close to the spa height:

 

[Phantom Of Utopia]

Something like this would have normally been in an air line that close to the spa height:

View attachment 426114

 

[Phantom Of Utopia]

Makes sense. So you would just push it in, tighten it (which would press against the inside of the pipe). To take it out, you loosen it and it comes right out. Fits inside a 1.5 inch pipe.
What's it called, where can I get one? I presume I can install it at the top of the air pipe ... is there something that keeps it from slipping down the air pipe (especially during installation / removal)?
I suppose I could just cut a piece of 1/2 inch PVC pipe and leave it inside the 1.5 inch pipe to keep it from slipping down the air pipe ... it might prove challenging to fetch if it fell down the pipe.