15+ year old hayward pump Leaking (Sp2805x7) at union, help

[MilPool]

Bought a house with a pool, last year we replaced the liner, as the former owner of the house stated that it was replaced 10 years ago, but the contractor said that the liner was close to 20+ years. This year the pump appears to be causing the issue. I was attempting to vaccum the pool for the first time, and noticed that the moment I attached the hose, I was getting air in the line. Isolated the problem to the union elbow, (spx1485b3), the coupling and sight pipe on the elbow was probably as old as the pool, and the o-ring was causing some water to leak and air to enter.
I opened the packaging, tossed on some nylon tape to the threads and attached it to the top of the pump. I tightened the coupling down with large pipe wrenches, to the point where I am afraid to tighten any further as I may damage the pump. However it is still leaking, actually more now. See the pic below.
http://imgur.com/w7JnAJ5

question to you, is there an o-ring where the union and the top of the housing meets? Do I need to even tighten the union further? do i need to take it off and add the nylon thread better?
The leak is small enough to filter the pool, but I cannot use it to vaccum or clean.

 

[danpik]

In your picture, the "lower" (smaller) nut is part of a threaded fitting that threads into the pump housing. This would have thread sealant on the threads to keep it from leaking. The upper (large) nut is part of a Union and the threads on it do not get sealant of any type. The design of the Union mating surfaces are what seals it. It can either be a taper fit between the two sealing surfaces or it will be two flat surfaces with an "O" ring between them. All of the unions on my pool seal fine hand tight.

What part is actually leaking?

 

[MilPool]

The union between the lower nut and the pump housing is where the water is leaking. The fitting wasn't tapered, I have a feeling that an o-ring might have let go. I'll have to disassemble and retry tonight.

 

[jokaankit]

I think danpik explained it well. The top nut where the union is tightened relies on an o-ring. Many times thats all that needs to be reseated or replaced. Since you mentioned you isolated the leak where it threads in you have to unthread, clean, reseal, and re-tighten. Do make sure thats where the leak is, because a leak from the union might look like a leak below at the threaded connection.

 

[danpik]

The threaded joint between the pump and lower nut is not a union. I theory, the threads of the two parts should tighten enough to seal properly. Pipe tape/pipe dope is used more as a lubricant to allow the threads to tighten further. The sealant will help seal the threads as well

Here is a picture of a dis-assembled union. Note the O-ring in this one. This is the seal. There should be no need to put sealant on the threaded portion as this is not a sealing surface. This coupling does not have to be over-tightened.



This is the male pipe coupling that is threaded into the pump housing. The threads should have at least 1-3 wraps of Teflon tape on then prior to assembly. It is important to wrap the treads properly. To do this, when looking straight into the fitting from the threaded end, the tape should wrap clockwise.