What does a Twin Ell do that a tee cannot?

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Bfordmn

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Hello:

I did a search on twin ells and did not find an answer to my question. I am installing a Grohmix valve for a combination tub/shower set up with a diverter spout. Only one of the two valve outlets can be used and will be using the lower one and plugging the upper one. The instructions specifically call for a twin ell to be use at the diverter spout.

It is my understanding that the twin ell reduces the likelihood of the showerhead dripping when the spout is in use. What is inside of a twin ell that makes it different than simply installing a tee somewhere between the valve and the spout? I would be surprised if there was any type of active device in the twin ell to reduce the diversion to the showerhead when the spout is being used.

My local big box stores had never heard of a twin ell, so I would like to complete the installation without making a trip to a specialty plumbing supply house, if possible.

All of the connections are 1/2", except the diverter spout that can be used with half or 3/4". A further option, beyond using a half x half x half tee, I could use a half x half x 3/4" tee, with the 3/4" going to the spout. That would even further reduce any potential backflow to the showerhead during the tub filling.

Any thoughts on twin ells would be greatly appreciated. Thanks.
 

Asktom

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A twin ell forces the water towards the spout, opens up larger to the spout and is small going to the shower. A 3/4" X 1/2" X 1/2" tee might work. A twin ell will work.
 

hj

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quote; would be surprised if there was any type of active device in the twin ell to reduce the diversion to the showerhead when the spout is being used.

It is NOT an active device, it is a design feature using different sized ports for the three connections. It is the ONLY way to prevent water from coming out of the shower head while filling the tub. A 3/4 x 1/2 x 1/2 tee WILL not do the same thing. Sometimes 3/4" diverter spouts (which is what you will need), come with the twin ell, otherwise a specialty store, such as Great Indoors, may be YOUR only source. I have several places where I can get them but not all will sell to the consumer. Actually, the source of your Grohe valve should have them.
 

Bfordmn

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Thank you, gentlemen, for your thoughtful and timely replies.

I did not want to wait to get the twin ell, because I thought I would get to plumbing the shower today (Sunday) and I knew I would not be able to find one on a Sunday. But, like all of my projects, everything takes twice as long as I think it will and the plumbing will get done on Monday or Tuesday night.

I look forward to getting a twin ell, so I can see what's inside and decipher the magic that only it can work.

Thanks again,
Ben
 

hj

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You will see a "large" opening from the front top connection, then a second, sometimes smaller, one below it to the rear shower connection. The "large" opening restricts how much water goes to the spout. The 3/4" spout can accept that much water without creating a restriction which would send water up the shower riser. A tee, which does not restrict the incoming water does not have the same dynamics.
 

Bfordmn

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I called around this morning to 4 or 5 plumbing wholesalers and none had a twin ell. Then I called Grohe tech support. Evan said that it would be just fine to use a set up as I had described in my first post. He said the twin ell was nothing more that a tee with an elarged flow to the spot and a reduced flow to the showerhead.

I know this is contrary to what others have posted. If the part were readily available, I would buy it and move on, but it's not. My house has very low water pressure to start with (top of hill) and I will fully test the set up before I cover up the wall. I will let you know how it turns out.

Thanks again,
Ben
 

hj

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Your Grohe "tech" had absolutely no idea how a twin ell works. Your tee is going to have a "super" enlarged flow to the spout, which even a 3/4" spout will NOT be able to handle, regardless of the flow to the shower head, which in the case of a tee is the same as to the spout. If it does not come out of the shower head, it will be because of your low pressure, NOT because the tee and twin ell are equivalent.
 

Bfordmn

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Thanks, HJ,

It sounds like you are saying that the flow from the valve needs to be restricted even further than 1/2" to reduce flow to the spout/showerhead even further. It also sounds like you are saying that the path back to the showerhead should be restricted to something less than 1/2" as well.

In your estimation, what size are the two restrictions (3/8", 1/4")? If one were to match the restrictions found in a twin ell with similar inline restrictions from both the valve and back to the showerhead, wouldn't that create a condition equivalent to a twin ell?

Given that a twin ell reduces the flow to the spout down to either a 3/8" or, even, 1/4" to eliminate the backflow to the showerhead, I have concerns about the flow rate to the spout and the time it will take to fill the tub. Maybe I should be looking into a diverter valve, instead.

Another idea that would get maximum flow out of the tub spout would be to use a tee arrangement as described in my first post and, then, simply use the volume control lever on the valve to reduce the flow if dribbling is a problem. That would get maximum flow to the spout, rather than the arbitrary reduction imparted by a twin ell.

Thanks,
Ben
 
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hj

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The path up to the shower does not HAVE to be restricted, (in fact its size is completely irrelevent), as long as the flow INTO the twin ell is reduced to the amount which the diverter spout can handle. That is the reason that the twin ell outlet is ALWAYS 3/4" and you have to use a 3/4" spout, not a 1/2" one with a 3/4" increaser. In the "old days", Chicago Faucets came with a 1" outlet and diverter spout.
 

Bfordmn

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Finally, I got this view of a twin ell from a Kohler tech. It appears to have 1/4" orifices from the valve and to the shower head. It is no wonder that nothing backflows: its choking the flow from the valve to a flow that is approximately 25% of the flow from a 1/2" pipe.

As I stated before, I don't like the idea of reducing the flow to my tub spout to that degree. First, since it is simple, I am going to try the set up using the tee and see how my reduced water pressure or valve setting effects the back flow. I will test that fully before closing up the wall and if I am not satisfied with the results, I am going to buy a dedicated valve diverter and a non-diverter tub spout.

Thanks again for all your help.
 

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The Plumher

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It's more about where the twin ell is located, close to the spout. The mixed water is taken down to it. It can either exit through the spout or travel up to the shower. It'll take the path of least resistance - the spout. When the diverter spout is engaged the water has no choice but to go to the shower.
 
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