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 Post subject: Boiler check valve lift
PostPosted: Mon Oct 17, 2016 11:25 pm 

Joined: Wed Oct 31, 2007 10:40 am
Posts: 69
Location: Chama, NM
Most of the repair instructions I have found for boiler check valve re-seating or replacement of valve parts say to be certain to maintain the original valve lift. Obviously good advice, but I have been unable to find information that tells what that should be for a given size and design of check valve.

I would think that there would be standard lifts for the various size valves, possibly differing somewhat depending on if it is a tapered or flat seat design. Presumably each manufacturer had their own specifications but it seems unlikely that they could vary much.

Specifically, I am looking for the proper lift for Hancock 2", flat seat, top mounted boiler check valves. Are there any resources out there available that contain this information?

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Russ Fischer
Cumbres & Toltec Scenic Railroad


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 Post subject: Re: Boiler check valve lift
PostPosted: Tue Oct 18, 2016 6:23 am 

Joined: Tue Sep 14, 2004 7:52 am
Posts: 1240
Location: Strasburg, PA
I can't help with manufacturer's specifications, but the rule of thumb I have always followed is:

You want to set the lift at 1/4 of the inlet diameter, in your case, 1/2" lift for a 2" i.d. Inlet. At that lift, the area between the open valve and seat equals the area of the inlet. I.e. 2"x3.14x.5"=3.14 sq.in. lift area. 3.14x1"^2=3.14 sq.in. inlet area.

Any lift over 1/4 of the inlet diameter is lost motion.

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 Post subject: Re: Boiler check valve lift
PostPosted: Tue Oct 18, 2016 9:38 am 

Joined: Sun Aug 22, 2004 8:35 pm
Posts: 374
The next question becomes;

How do you check the lift when all of the parts are internal?

I like to use lead sheet. I have also made soft lead ingets that can be placed between the cap and check. When you seat the cap, the lead is crushed between the two. Take it apart again and measure the crush.

Believe it or not, these parts do wear out and excessive travel is an issue. I found the most common issue related to excessive travel is a valve that will not seat, or that jams when trying to seat. This then causes hot water to leave the boiler, making its way to the injector, heating the injector causing to fail or break.

Written on my phone while waiting on a plane. Please forgive and blunders.

Kindly,

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John E. Rimmasch
Wasatch Railroad Contractors


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 Post subject: Re: Boiler check valve lift
PostPosted: Tue Oct 18, 2016 9:53 am 

Joined: Tue Sep 14, 2004 7:52 am
Posts: 1240
Location: Strasburg, PA
John E. Rimmasch wrote:
The next question becomes;

How do you check the lift when all of the parts are internal?

The quick and easy method I use (though less precise) is to stack flat washers on top of the valve disk until the cap won't seat. The height of the washer stack is the lift of the valve.

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"It was not easy to convince Allnutt. All his shop training had given him a profound prejudice against inexact work, experimental work, hit-or-miss work."
C. S. Forester

Strasburg Rail Road Mechanical Department


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 Post subject: Re: Boiler check valve lift
PostPosted: Tue Oct 18, 2016 10:29 am 

Joined: Sun Aug 22, 2004 7:19 am
Posts: 5254
Location: southeastern USA
You can make a gauge like the WABCO air compressor valve lift gauge to suit your checks. Takes a lot of the guess work out of the equasion. Now, how about wear clearance around the vanes on the poppet?

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 Post subject: Re: Boiler check valve lift
PostPosted: Wed Oct 19, 2016 1:18 am 

Joined: Sun Aug 22, 2004 8:35 pm
Posts: 374
Tried the Kelly washer trick. I ended up glueing the washers together as they came apart of the cap twisted them off the valve when seating. Also tried heavy sculpting clay, results were as accurate as glued washers.

Valve flute wear; I don't have my books with me but I think it was 1/16 for some heat expanssion. The water lubricates the valve a bit. Once it wears to the point that it wiggles in the body, it is too loose. If it is allowed to rise too high, and wiggle, it will jam. Keep in mind, the flutes with wear tapered and some are machined that way. Best tokeep it as spec. as possible.

Again, on my phone, please forgive my heavy fingers

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Wasatch Railroad Contractors


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