Sealing Valves 1

[Hayden]

I've recently started a job designing valves. I've been presented with a problem which I'm sure is very common. We have a meter with a housing and a flat top cover. The cavity the cover covers is about a trapezoid of about 6" x 10" x 4". Both parts are cast and to be machined later. 8 Bolts hold the 2 together.

This valve is to work at municipal water supplies up to 16 Bar.

I've been asked to look at a way of sealing the housing and top cover. We have 2 main options;
Cutting a groove in the cover to house an 'o' ring,
Using a gasket between the 2.

There are concernes that a rubber gasket could burst under peak pressure. Is there any benefit using a composite gasket?

I'm new to this field and would like any input on other methods that could be employed for sealing this assembly. Unfortunately I only have a day to try to find something before we take a punt with the rubber gasket design.

Thanks for your help.

Hayden

 

[Cockroach]

By far, your choice for superior seal capacity is the o-ring application. Although you are holding very little pressure, roughly 232 psi or ANSI Class 150 application, a gasket would work but present other problems such as bolt torque requirements, secular compression set loss, etc.

Given your geometry and depending on your bolting pattern, a preliminary o-ring groove could be cut 1/8 inch inside the perimeter of your "trapazoid" cover, just inside the bolting perimeter. Containment pressure is low, therefore select a Class 100 elastomer, 0.103 cross section with an inner diameter near 7.237 inches; this is #168 on the commercial available Parker-Hannifin scale. The geometry of your groove should be such that the ID of the path corresponds within 1/2% o-ring stretch. Gland depth should be 0.074/0.080 inches, thus providing 25% squeeze upon make-up with the cover.

I suggest using a generous fillet along the path of the o-ring groove, maybe 1/4 R or so. This will help in keeping the elastomer in the recess as the cover is flipped to be bolted in place.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[tothepoint]

O-ring sealing as suggested above is your best choice given the application and temperature. This is a fairly large cover that the internal pressure is working against. Make sure that you have adequate bolting capability to counteract the hydrostatic end force. Base your assembly bolt load on the hydrostatic force, and not just O-ring squeeze.