When to use washer/gasket vs. thread sealant?

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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thesharpener
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#1: Post by thesharpener »

I have a general question on sealing various fittings in espresso machines - I am trying to make sense of when thread sealant should be used (be it a loctite/loxeal product or teflon tape) versus situations where a copper/fiber/teflon sealing washer is appropriate. For example, in the check valve/expansion valve assembly pictured (please forgive my horrendous rendering), some of the mating parts have copper washers which I assume helps form the seal, and others are just screwed together, I assume with some sort of thread sealer.



Searched the site a bit and found a few forum topics that discussed this, but can't find a definitive approach.

My understanding is that the BSP parallel threads don't seal when screwed together (like tapered threads), so I my best guess is that fittings that mate with threads only should have some sort of thread sealant? Am I on the right track or am I way off on this?
Pete - LMWDP #572

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Peppersass
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#2: Post by Peppersass »

First off, tapered threads do require Teflon tape or thread sealant. More on that below.

I'm not an expert, but here's what I've gathered from various sources:

1. BSPP threads, which are common in espresso machines, are parallel and require a copper/fiber/Teflon washer to seal. Though not usually found in espresso machines, some BSPP fittings are designed to use O-rings, which can be surrounded by a metal washer. In such cases, the O-ring has to be of the appropriate material (e.g., Viton) if used to seal a high-heat joint.

2. I know of at least one espresso machine dealer who uses Teflon tape or liquid sealant on BSPP fittings as an extra measure in case the washer doesn't seal. This may be necessary if the washer has been used previously. As far as I know, there's nothing wrong with doing this, but you have to be careful to apply the tape or sealant so that none of it gets into the tubes. That could cause clogs and massive headaches downstream. Ideally, you should use a new washer of the appropriate type and torque the fitting according to spec.

3. Some female BSPP fittings in espresso machines connect to copper or stainless tubes that have "nipples" brazed into the end that are secured to the BSPP fitting with a large nut. These connections are self-sealing and don't require a washer or thread sealant.

4. BSPT threads, which I've not seen in in espresso machines, are tapered and require Teflon tape or liquid thread sealant to seal. They are similar to NPT fittings (see #3), but the taper angle is different.

5. NPT threads, which I've never seen in an espresso machines (except as adapters for external plumb-in connections), are tapered and require Teflon tape or liquid thread sealant to seal.

6. Male JIC flare fittings are used in some espresso machines (e.g., they're used on the steam valve and 3-way valve in my GS/3.) They're used to connect a tube, the end of which has been pressed into a female flare. The connection is secured by a large nut. These connections are self-sealing and don't require a washer or sealant. However, you do have to be careful not to torque the nut too tightly or the female flare will deform or break off. JIC fittings have the same threading as BSPP fittings. The angle of the flare isn't compatible with flare fittings you can buy in US hardware stores, which I think have an SAE 45-degree angle.

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bluesman
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#3: Post by bluesman »

Peppersass wrote:The angle of the flare isn't compatible with flare fittings you can buy in US hardware stores, which I think have an SAE 45-degree angle.
Great answer!

One addition: there are both SAE and metric compression flare fittings, and neither is a perfect mate for the other even if they seem to fit together. I think there were also Whitworth flares. SAE flares are indeed 45 degrees. But the standard AN flare is 37 degrees with the same nut sizes, Komatsu and metric (which are not interchangeable) are 30, and DIN flares come in 24 & 60 degrees. Be careful!

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thesharpener (original poster)
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#4: Post by thesharpener (original poster) »

Thanks David and Dick for the informative replies. I've only worked on two small Olympia machines, and these exclusively use the nipple style compression fittings. I've recently picked up a few large, old, commercial machines to fix as learning projects and have encountered some fittings I'm not familiar with.
Peppersass wrote:1. BSPP threads, which are common in espresso machines, are parallel and require a copper/fiber/Teflon washer to seal. Though not usually found in espresso machines, some BSPP fittings are designed to use O-rings, which can be surrounded by a metal washer. In such cases, the O-ring has to be of the appropriate material (e.g., Viton) if used to seal a high-heat joint.
In the case of the assembly I pictured in my original post, the connections that are just threaded together with no washer (all 1/8 BSPP), is it possible that the fitting itself has a sealing surface so a washer is not necessary?
Pete - LMWDP #572

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bluesman
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#5: Post by bluesman »

thesharpener wrote:In the case of the assembly I pictured in my original post, the connections that are just threaded together with no washer (all 1/8 BSPP), is it possible that the fitting itself has a sealing surface so a washer is not necessary?
There are so many different kinds of adapters and couplings that anything is possible. There are BSPP couplings with "captive seals" like this one and this one. There are flared-end couplings with parallel threads that hold a male convex seating area against a female concave mate like this:



and there are similar fittings with an integral O-ring instead of a tapered seat interface as the seal:



But these are all expensive, and I've never seen such a fastener in an espresso machine unless an enterprising tinkerer modified it. Of course, I can't imagine that anyone would do such a thing to a perfectly good espresso machine..... Image

It's also possible (although unlikely) that whoever assembled those joints simply forgot about or didn't know enough to use a sealing device or medium. I'm always amazed at the fact that improperly built equipment often functions despite errors - the "bigger hammer" theory is only proven wrong when the object of such attention breaks.

bettysnephew
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#6: Post by bettysnephew »

From a total reliability standpoint, when I worked as a maintenance mechanic we doped every fitting that was not a tubing flare or compression seal type. If it was thread to thread it got a bit. It can't hurt to be a belt and suspenders kind of guy. It also reduced galling when later disassembling the fittings but almost every fitting we used was stainless to stainless which is notorious for seizing together. It can't hurt to use a judicious amount of sealer just don't slop it on.
Suffering from EAS (Espresso Acquisition Syndrome)
LMWDP #586

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Peppersass
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#7: Post by Peppersass »

thesharpener wrote:In the case of the assembly I pictured in my original post, the connections that are just threaded together with no washer (all 1/8 BSPP), is it possible that the fitting itself has a sealing surface so a washer is not necessary?
To answer that question, you'll have to unscrew the fittings and see what their ends look like and what's going on inside the tubes they mate with. One or both of them could be a male flare fitting that seals against a concave surface inside the tube. Or, someone might have used thread sealant instead of a washer because they didn't know better or the right size washer wasn't available.