when does a gramophone face need re-machining?

[Thirlmere]

Hi Guys, just came across a 16" Class 600 expanding gate valve, and there doesn't appear to be much gramophone face on there at all.
Maybe it was never very deep, i don't know. But the finish on the face is certainly not to the specs i have.

My drawings specify 45 - 50 serrations per inch.

Are there any standards to check so that i can tell when a gramophone finish needs re-machining?

Thanks

 

[gerhardl]

The purpose of the serrating is of course, togheter with the flange sealing material, to ensure the correct geometric compression and sealing between the flange and counter-flange surfaces.

Advice: first check that you have the complete and correct description of valveflange (serrated or flat), sealing type (gasket or o-ring), and counterflange (serrated, flat or flat with groove for o-ring) and complete norm description with drawings of details for all parts.

As the valve-flange is only a lesser (but important!) part of the sealing, any modification of the valve-flange will influence the total sealing, and should be done in accordance with the end-users norms and/or wishes.

 

[ricklts]

I assume you are referring to a 16" ANSI 600# Raised Face end flange with spiral cut grooves? The grooves, unless otherwise specified by the client, should be cut with a 0.006" Round nose tool, such that the resultant finish is in the 125 to 250 RMS range. Depending on service and gasket design, my preferences have been for the slightly rougher RMS 250 finish, as it allows the gasket filler material to 'flow' more readily.

What gasket is to be used? Operating conditions may dictate a different gasket design or materials.

 

[moltenmetal]

We've found that a 40-55 grooves per inch pass with a 1/16" radius tip toolbit can also generate the required surface finish. With the larger radius toolbit, the depth of cut per pass doesn't matter, since the passes interfere with one another to result in the desired surface roughness.