Gate Valve Repair 3

[JAlton]

I need information on "How to fit a Wedge" in a Gate Valve.
I understand it requires Feeler gauges to determine how much metal to remove, but I need details. Can anyone help?

JAC

 

[scalleke]

Make sure the seat faces are properly lapped.

Make sure the wedge surfaces are nicely lapped

Place the wedge in the valve solidly down and against one of the seats.

With feeler gauges determine the gap between the opposite seat and the wedge surface. Also determine the largest gap postion on the seat.

Grind the seat face down by 0 on the place where you found the max gap and by the amount of max gap that you found 180 degrees from the position where you measured the max gap.

By simply placing the wedge between the seats and using a valve stem you can tap the seat to get a contact mark which will give you an apprehension of the health of the valve.

Best Regards,

Scalleke

 

[JAlton]

Very good. I understand, remove zero metal from largest gap location and an amount equal to the gap from seat area 180 from gap.

Do you grind the seat ring in the valve or grind the seat area of the wedge?

Also, do you use bluing to get a contact mark?

Thanks.

JAC

 

[JimCasey]

It is also possible to weld an overlay on the seating surfaces. This builds up any wire-draws or other material loss, then you grind it true. The grinder I have seen used was a 1/2" thick plate with contact-adhesive attached abrasive sheet. It had a strut attached to the shaft bearings, and a bicycle-chain drive to a similar shaft on the othere end of the strut outside the valve. As I recall it was driven by a drill motor, But it was clamped in place to maintain an accurate angle. Like all grinding operations: take the big chunks off with coarse abrasive, then progressively finer grits until the surface finish is what you need.

 

[scalleke]

Usually the wedge seating surface is ground.

This is easier as any surface grinding machine can be used for this purpose.

What is difficult is that the seating surface on the wedge must be lapped after grinding on a lapping plate.

Do note that the wedge is heavier on the top section and that during the lapping you will remove more material at the top section. You can compensate for this by placing a small counterweight near the bottom section on top of the wedge during the lapping.

The seats can be ground or lapped in the valve. However the seat profile can be disturbed if you do this and I would not recommend it, the seat profile being one of the design features of the valve.

However do inspect the sealing surface of the valve seats. If you have any doubts about the surface condition the seats can be lapped. Use a disk with emery cloth for rougher material removal and work your way to finer and finer grades to get a smooth finish. Here too lapping compound can be used if you need to.

No need for blueing to get the contact mark. Blue will smear more than show you things. Tap the wedge in place, remove from the valve (Pull on stem while lightly tapping the valve body) and hold the wedge sealing surface under light to see the contact mark looking at the surface.

Contact mark must be nice and round on both sides and width of the mark must be even all around.

Look at the contact mark on the seats too.

Best regards

Scalleke