What size o-ring for 3/8" sight glass and 3/8" compression fitting?

Sorry if this has been posted before, but I have searched for a while and couldn't find the answer. I'm wondering if someone could tell me what size silicone o-rings will work in place of the ferrule in a 3/8" compression fitting when installing a 3/8" sight glass tube.

thanks!

 

See here: http://www.bargainfittings.com/index.php?route=product/product&path=42&product_id=106.

3/8" ID x 1/2" OD

 

Sure, you need a 3/8" ID o-ring to slide onto a 3/8" OD sight glass, but do the o-rings on that website fit and seal when put in a 3/8" compression fitting? I don't see any mention of a compression fitting.

Basically I need whatever size these o-rings are: http://www.bargainfittings.com/index.php?route=product/product&path=45&product_id=117

They say that they are 3/8" ID, but they don't specify what the OD is.

 

You can use the nylon ferrule.

 

If you look at their o-ring page http://www.bargainfittings.com/index.php?route=product/product&path=42&product_id=106 it's gotta be the 3/8" ID x 1/2" OD. Also just eyeballing the picture the thickness of the ring looks to be about 1/6 of the ID or 1/16", so I'm comfortable asserting 1/2" OD.

Edit: Alternatively, I'd be hard pressed to find an instance where Bobby gave bad advice.

 

I would, but mine came with a metal ferrule, so I need something else. If I think the 1/2" OD o-ring will fit inside of my compression fitting, I'll get some of those 3/8 x 1/2" o-rings and see how it works out. Didn't you used to sell sight glass kits with silicone o-rings for sealing in the compression fitting? If so, did you use 3/8" x 1/2"?

 

What I'm saying is that you can grab a nylon replacement ferrule at home depot or Lowes to avoid ordering silicone orings.

If you want the orings, I'm pretty sure I used -010, 1/4" ID x 3/8" OD stretched over the 3/8 tubing. If you measure the ID of the compression nut, I think you'll find that a 1/2" OD oring won't make it.

 

Bobby,
That is exactly what I kind of suspected. Thank you so much. I did not know that you could buy just a nylon ferrule by itself, so that little tid bit is also much appreciated! Thanks for the great idea!

 

The oring sized 3/8" Tube - 3/8" ID x 1/2" OD is what we ship with our sight gauge kits.

A nylon ferrule will work as well.

I just checked on this and it looks like the Anderson Metals brand (model 00560-06) ferrule is made with Delrin Plastic and has a melting point of 347
I'll probably test these and start stocking them.

Looks like watts brand is also made of Delrin. Working temp goes to 250 degrees on both brands

 

Thanks, BargainFittings.

I picked up the Delrin ferrules at Home Depot because it was easy, although I'm going to get some o-rings from you when I place an order for some other stuff to see how I like them. I am surprised that they are 1/2" OD, though. The inside of my compression nut measures exactly 0.500", but the opening of the tapered part of the fitting (where the ferrule would normally reside) measures quite a bit less than 0.500"... something around 0.450" if I remember correctly. Have you ever noticed that an o-ring got sliced by the sharp edge on the top of the tapered surface after you took a sight glass apart? It's probably not an issue...

 

The threads on the compression nut will eventually nick up the edge of the orings if you take it apart often but the good news is that it doesn't affect the sealing surfaces at all. The curved surface of the bottom oring nestles into the taper of the fitting. Any orings you stack on top of that are just to take up the space between the bottom oring and the top of the nut.

 

As Bobby said the o-rings stack and take up slack in the compression nut.

Let me know how you like the Delrin sleeves. It might be awhile before I get to test them.

 

Wayne,

Just to update the thread- The Delrin ferrule has worked perfectly. I have not taken it apart since I put it together 9 months ago. There have been no leaks whatsoever.

 

Thanks for reporting back.

I stock the 1/2 and 3/8 delrin sleeves now.

 

With the delrin sleeves I just ordered from you Wayne, do you need to use these with any other parts? The compression fittings I have have the two ferrules?
Sorry for bringing up an old post

 

A single delrin sleeve works by itself.

You can use the smaller of the two rings if needed.

The delrin sleeve replaces the larger stainless sleeve.