Gaskets

[Boiler BriParticipant @boilerbri]

I have just finished my casting for my 4" DNY traction engine. I have all the studs tapped and have now turned my attention to fitting the casting to the boiler pad.

I have some 1/32 gasket material and wondered? Do i make a full gasket or one that is an inch or so in from the edges.

Do you then put some gasket sealer on it or leave it dry. I have a good fit so maybe the gasket will squash down and seal?

Your thoughts please.

Bri

[Boiler BriParticipant @boilerbri]

[Boiler BriParticipant @boilerbri]

No experts on this subject then??

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

Hi Bri ,

This is an endless subject but here's a few thoughts to begin with :

(1) Far better not to have a gasket at all where possible . Follow common full size practice and bed cylinder to mounting face accurately by blueing and scraping and then (apart from some sealant ) bolt down metal on metal .

(2) If using a gasket this should be made to the full footprint of the mating surfaces – just like an old type car cylinder head gasket .

Gaskets only work properly if the mating surfaces are quite accurate – although its often done gaskets should never be used to compensate for poorly finished mating surfaces .

Clearance holes for bolts or studs should give adequate clearance be and well finished – stray burrs and bits of broken off gasket can cause all sorts of difficulties .

(3) Best material for a gasket is freshly annealed copper sheet . Personally I would never use soft gasket material for such an important pressure holding and structural joint as the cylinder to boiler one .

(4) When fitting gaskets properly it is always best to do a bedding down test . Easiest way is to make a cardboard gasket replica , bolt it down hard and then remove and examine . Imprint should be nice and even everywhere with no gaps or scrapes . Any flaws can be traced back to some defect in the mating surfaces and corrected .

(5) When bolting down finally use a stress balancing procedure . This is again like bolting down a car cylinder head . Tighten one up then one approximately diagonally opposite , then rotate one position and repeat etc going round several times until all are tight and all the same to feel . Ideally use an aerospace torque wrench and decide beforehand a set figure for your torque .

(6) After natural settling down and initial steamings the bolts will need rechecking and probably further tightening . Full size practice in olden times was to do final torque down in steam but I would positively not recommend that practice now on safety grounds .

There's several more volumes of this – ask any questions you like .

Regards ,

Michael Williams .

[JDEngParticipant @jdeng]

Bri,

I'd make sure first of all that the gasket material you have is correct for steam. Check with a company such as Heritage Steam Supplies; they specialise in this field and will advise you what is the best material for the job. Personally I can't see any harm in a soft gasket in this application but I would ask and be guided by the experts. They use soft gaskets around the top and bottom of Sentinel boilers and they operate at a far higher pressure than you will be concerned with.

I would use a graphite jointing compound such as Foliac (made by Rocol); smear it on both sides of the gasket. Personally I'd stear clear of Stag or Manganese paste, it sets like concrete whereas Foliac is fairly easily removed if you ever have to remake the joint.

Knock out the bolt/stud holes in the gasket before you knock or cut the edges to size; if you do it the other way round you may break the gasket.

Hope this helps.

John.

[Author]

Posts