Displacement lubricator and safety valves

Displacement lubricator and safety valves

This topic has 7 replies, 4 voices, and was last updated 12 December 2025 at 15:08 by JasonB.

Viewing 8 posts - 1 through 8 (of 8 total)

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12 December 2025 at 06:14 #828437
Brian John
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@brianjohn93961
1. I have been absent from the hobby for a few years and I noticed that the displacement lubricators that I purchased from PM Research in the US have lost their ”rubber” rings on the valve/control wheel. They have rotted away. What can I use to replace them ?

2. In the past I used Mamod safety valves on my home-made boilers (tiddlers – very low pressure) but I have found that Mamod have gone broke. Is anybody making replacement safety valves to fit all the Mamod machines still out there ?
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12 December 2025 at 07:19 #828443
JasonB
Moderator
@jasonb
Hello stranger

I think PMR just use small O rings stretched onto the brass central wheel so you should be able to measure the cross section and work out the diameter then order online from a bearing or seal supplier of Australian ebay.
12 December 2025 at 08:21 #828447
Weary
Participant
@weary
Mamod safety valves available on ebay and loadsa other places.

There is a Mamod Owners Group on facebook if that is your thing & they will give you plenty of leads.

Phil
12 December 2025 at 08:23 #828448
Brian John
Participant
@brianjohn93961
Nitrile rubber – oil resistant ? Or is there something else more suitable ?
12 December 2025 at 09:04 #828449
JasonB
Moderator
@jasonb
Go for Viton it resists oil better. Sometimes also sold under the name FKM
12 December 2025 at 13:38 #828502
Nigel Graham 2
Participant
@nigelgraham2
1) The stockists of seals etc often have charts showing O-ring grades suitability by application.

2) If necessary, carefully and non-destructively analyse an existing Mamod valve from one your models, and copy that.
12 December 2025 at 14:22 #828507
Brian John
Participant
@brianjohn93961
Can these also be used as piston rings in steam engines ?
12 December 2025 at 15:08 #828511
JasonB
Moderator
@jasonb
Yes they are OK for iston rings in both steam and IC engines
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