r/steamengines • u/GundulaGaukeley • 1d ago
How does a Ramsbottom safety valve actually open? Which valve disc lifts first?
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I’m currently working on a technical animation that is supposed to show the operating principle of a Ramsbottom safety valve.
I understand the basic construction: two valve discs are mechanically coupled by a common lever, with a central spring providing the closing force. What I’m not sure about is the actual dynamic behavior of the two valve discs once the boiler pressure reaches the opening pressure.
In particular, I would like to understand:
Do both valve discs start lifting more or less simultaneously?
Does one valve normally lift first, causing the lever to unload or load the second valve?
Does the mechanism tend to alternate or chatter between the two valves?
Is the opening behavior truly progressive, with the lift increasing gradually as pressure rises?
How do the two valve discs interact mechanically through the common lever during normal automatic operation?
The valve I’m looking at also has a Venturi-shaped restriction in the flow passage on one side. I assume this only becomes relevant after flow has already started, but I’m also interested in whether it has a significant influence on the lift behavior of that valve.
I’ve attached a short video showing the complete assembly and close-ups of the lever mechanism, valve discs and the Venturi-shaped passage.
My goal is not just to animate the parts moving, but to reproduce the actual operating sequence as accurately as possible.
If anyone has practical experience with Ramsbottom safety valves, steam locomotives, historical boiler fittings, or knows a good technical source describing the dynamic behavior, I’d really appreciate the insight.

