I am looking for some advice on repairing double seat throttle valves. After spending a couple of hours lapping in our throttle valve and having less than stellar results I have been wondering if anyone has built up the faces on the valve with brazing? Our valve is pitted and worn concave.We are in the process now of looking for our throttle valve pattern so we can cast and machine a new valve, but in the meantime I am thinking about building up the faces with braze and machining and then lapping in. Has anyone tried this? thanks, Rick.

enginman@gis.net

I have heard that some have machined new valves from stainless, probably 316 but I am not sure of that. No comment on the brazing however I think that the seats are to built up with stellite. Lapping in a double seat dome throttle valve is a bit tricky if you haven't done it before.

I wouldn't attempt to braze up the seats. The slightest porosity or defect will turn into a steam cut in no time. Worn concave and pitted seats are not that unusual. As long as you can lap a complete ring into each seat that is wider than the widest pit it should seal.

The biggest problem is getting the seats into proper relationship with each other. Once both are lapped to a satisfactory finish, clean the bottom seat with solvent, and oil it. Apply more fine lapping compound to the upper seat only, and lap it a time or two more. The idea is to make the spool just a little taller than the valve body. With both seats clean and dry, you should be able to hit the top of the spool side to side with the heal of your hand and hear a slight click, as in rocks back and forth a tiny amount.

Patience is your best tool here. Don't bear down on the spool as you lap. Don't drive the spool with a motor to lap it. Add new compound about every minute, and done be surprised if it takes all day. Also don't be surprised if it leaks some when under steam. Double seat throttles are virtually impossible to make completely steam tight.

Hi Rick;

I have seen brazed buildup on some small saturated engines done before but it probably won't be the long term repair you want it to be.

If there is a lot of meat in the valve body itself, you could make a boring bar type of refacing tool if the seats are truly bad and cut new seats, followed by remachining the spool to match and lapping to a nice surface. That is a real fine machining job with hours of trial fitting, bluing, and fiddling.

If you don't have deep cuts, a long and tedious lapping job will probably work best and do less damage to the remaining material.

Either way, with the standard US spool design, it isn't going to be fast and easy.

Best wishes.

Dave

lathro19@idt.net

Rick;

I have just finished reading articles by Jack Anderson (Search the Interchange for his name) in one of my old L&RP magazines. His description of how to fit this kind of throttle valve is second to none.

It was in a L&RP from 1988 or 1989; details at home; email me if you want it.

(the parts of his series that I have are fantastic, I am trying to get the rest)

John Stewart
Ottawa

> I am looking for some advice on repairing
> double seat throttle valves. After spending
> a couple of hours lapping in our throttle
> valve and having less than stellar results I
> have been wondering if anyone has built up
> the faces on the valve with brazing? Our
> valve is pitted and worn concave.We are in
> the process now of looking for our throttle
...


john.stewart@crc.ca

> I have heard that some have machined new
> valves from stainless, probably 316 but I am
> not sure of that. No comment on the brazing
> however I think that the seats are to built
> up with stellite. Lapping in a double seat
> dome throttle valve is a bit tricky if you
> haven't done it before.
RK thank you for taking the time to respond to my question.Every little bit of info helps. Have lapped several throttles but I am wondering if I could improve my technique. Thanks, Rick.

enginman@gis.net

> I wouldn't attempt to braze up the seats.
> The slightest porosity or defect will turn
> into a steam cut in no time. Worn concave
> and pitted seats are not that unusual. As
> long as you can lap a complete ring into
> each seat that is wider than the widest pit
> it should seal.

> The biggest problem is getting the seats
> into proper relationship with each other.
> Once both are lapped to a satisfactory
> finish, clean the bottom seat with solvent,
> and oil it. Apply more fine lapping compound
> to the upper seat only, and lap it a time or
> two more. The idea is to make the spool just
> a little taller than the valve body. With
> both seats clean and dry, you should be able
> to hit the top of the spool side to side
> with the heal of your hand and hear a slight
> click, as in rocks back and forth a tiny
> amount.

> Patience is your best tool here. Don't bear
> down on the spool as you lap. Don't drive
> the spool with a motor to lap it. Add new
> compound about every minute, and done be
> surprised if it takes all day. Also don't be
> surprised if it leaks some when under steam.
> Double seat throttles are virtually
> impossible to make completely steam tight.
Thanks HKA for taking the time to respond to my question with such an informative reply. I usually like to back channel if I can. I was not completely happy with the bottom seat, that always seems to be the one that does not hit the best.Your suggestion of lapping the top so that the spool hits hard on the bottom and rocks a little on the top backs up what I was thinking I should do.Ultimately we will make a new throttle but the lapping process will be done to that also. Was only thinking of building up the faces on the spool and not the valve seats. Will give the lapping another try. Just want to mention I always look forward to what you have to say about the various topics that come up on this board. Thanks again, Rick.

enginman@gis.net

> I concur with HKA about the slight click, but be very careful that the click you hear is the top seat. The click will sound the same whether it is on the top or the bottom seat. Put one hand aganist the bottom of the thimble and against the throttle body and feel for movement when you tap against the top of the thimble with the other hand. This is a good way to assure the click is or isn't at the top seat. FYI, the click should only be about 1/1000". Good luck!

Muss405@yahoo.com

Still not mentioned in this link is the chance of having a new valve cast.

We have a shop in Salt Lake City that will cast the entire valve for (what I felt to be) a very small cost. The HVRR has two engines. We are looking at casting two new valves (complete) for each engine. These are Baldwin engines. If yours is a Baldwin, we should talk, I would consider working a deal where we all get new valves for a cheaper rate. Cost sharing if you will.

I agree with all that has been said. As a side note, I had talked about building up such a valve with a spray trans, type wire feed arc weld. This has been done and it has worked, the problem here is, when you begin to machine the valve seats, the new metal can peal off of the original casting. Then you must have a new one cast.

Regular arc welding is not really an option for many reasons. I agree with the brazing theory...one small pin hole with turn into a major steam cut down the line.

I would like to talk if you want to go the casting method..... e-mail me!

John E. Rimmasch
HVRR



jrimmasch@yahoo.com