Under Pressure! LMR Safety Valves

[What About The Bee]

Boiler safety was certainly a consideration for the LMR. There is plenty of visual evidence and the LMR safety record vis boiler explosions is fairly remarkable. There was only one boiler explosion and it was not attributed to failure of the safety valve. Patentee did explode, the failure attributed, by the LMR inquest, to the draw bar being connected directly to the firebox, the boiler torn asunder by the load up an incline.

There are two types of safety valves used by the LMR. The first is a Salter Safety Valve. Yes, that famous UK company, established in 1760, still in business today making weighing devices. The other is a Timothy Hackworth Safety Valve.

Rocket

Depictions of Rocket, LMR#1, do not clearly show the safety valve arrangement. We can see a column on top of the boiler, thats likely the Timothy Hackworth Safety Valve, in an enclosure. But for all the contemporary Rocket depictions, I cannot find one with the Salter Safety Valve.

The OO Hornby Rocket has a Salter Safety Valve (herein after SSV) installed, and probably a Timothy Hackworth Safety Valve (herein after THSV).

Issac Shaw, a known good observer, does show Northumbrian LMR#7 with an SSV.

Northumbrian was certainly a Rocket-Class locomotive and we can therefore expect that other members of class had a Salter Safety Valve.

This depiction of a Rocket-Class locomotive shows a THSV, as well as an SSV. Most unusually, the THSV is shown without the tall vertical tube.

How do they work?

Here are both safety valves

Both operate as a function of internal boiler pressure vs spring force. The valve itself is either open or closed. When the internal pressure exceeds the applied spring force, the valve opens. When internal pressure is less, it closes. The difference in valves is the spring itself.

The SSV is essentially a coiled spring scale, the initial product of the Salter Company in 1760. The long lever arm is used to gain sensitivity. Note that the top nut could be adjusted by the enginemen to change the trip point of the SSV. This complaint is noted by Pambour, Traite Practique. The enginemen did fiddle with the setting so as to manage steam pressure.

The THSV is a stacked set of leaf springs, directly applying force to the valve without levers. The following image of an 1830s survivor shows us 30, 40 and 50 psi graduations. Moreover, notice the distinct correlation between the survivor and Armengaud's mechanical drawing. This builds tremendous confidence in what I can observe in Armengaud's drawings.

https://www.scienceandsociety.co.uk/results.asp?image=10306470

 The LMR enclosed THSV in columns, to prevent tampering and, it is theorized, to vent steam above enginemen heads

Other Hornby Era 1

These do not show a THSV or even the tall columns above the boiler. Each has a set of two SSV. This is consistent with Lion, preserved at the museum. Hornby cannot be faulted for leaving the Timothy Hackworth Safety Valve off of Lion. The fault lies with the restorers of Lion, not with Hornby.

But what about other depictions of locomotives, what do they show?

Liver LMR26, an Edward Bury locomotive, is depicted with both a SSV & likely THSV. Note the Transitional Tender, Generation 2.

Patentee LMR 33 has both an SSV and clearly a THSV column.

Fury LMR#21, a Fenton and Murray locomotive, shows an SSV and likely a THSV in a short column.

Issac Shaw, a known good observer, depicts Planet. We can be sure that this is Planet, with the name evident in the depiction. Not a Planet-class, rather, Planet LMR#9, herself. By the firebox, the SSV is visible just behind the steam dome. The THSV is shown in the column, clearly venting steam overpressure.

This depiction of Planet-class locomotive clearly shows SSV and, by the height of the tall columns, THSV.

It appears that the LMR utilized both types, often side by side on the same locomotive.  

If you have these Hornby locomotives on your layout, you now know what some of the bits are!

Bee

[What About The Bee]

I have encountered a reference which denotes the locations if Rocket's safety valves and names them as safety valves. There is no clarification as to the type of safety valve.

Treatise on rail roads and internal communications Thomas Earle 1830

The annotated drawing has a blob of ink right by the F, making it appear to be a P. The descriptive text, inset for convenience, does not include a P.

The other competitors at Rainhill are similarly illustrated and annotated, for those who are curious.

Bee