Letting Off Steam: Importance of Control in Regulating a Spence PRV

The Industrial Revolution brought new ways of making things. Today’s technology wouldn’t have been possible without the era of assembly lines, sewing machines, combustion engines, and huge boilers. With these innovations, however, also came accidents like boilers exploding left and right.

Dan Holohan for ACHR News refers to one such accident: the explosion that destroyed a shoe factory in Boston in 1905. Among the remains of the factory was a boiler that flew several feet into the air in the ensuing explosion and landed right on the factory engineer’s front yard.

a history of steam pressure relief valves
Where were steam valves at the time? They were more than 200 years old by the time of the explosion. The modern Spence PRV (pressure relief valve) had benefited from centuries of constant evolution, even at a time when boiler explosions were part of daily life. The valves at the time worked splendidly, but there was just one problem.

The operating engineer could control the relief pressure of this crude device by moving the weight further out on the lever, or by adding more weight to the lever if the spirit moved him. Many did add weight because they didn’t want to lose the good head of steam they had worked so hard to build.

It seemed like steam, for the industrial worker at the time, was the blood of life. As far as history is concerned, however, it has always been.

From Food to Factory

Steam valves were conceived as a result of a related invention called a “steam digester.” Invented in the late 17th century by French physicist Denis Papin, this device became the precursor to pressure cookers. Using high-pressure steam, the steam digester could take animal bones and soften them up for making delicious jellies.

At this point, Papin knew that high pressure could become a precursor to a freak accident. This resulted in creating a device to regulate pressure by releasing it.

“Enormous strength was needed in the machine to stand the high pressure generated, and Papin found that he could only make his machine successful by contriving a mechanical device that would release pressure at a certain point and thus prevent explosion. This he finally worked out during 1681 with the first steam pressure safety valve.


Going back to boiler accidents, steam valve design at the time is hardly to blame. Investigations on various boiler explosions in the mid-19th century mostly blamed reckless management. It only takes a failed rivet for even the most robust of boilers to explode when anyone least expects it.

The modern Spence valve, in this case, won’t work well if it isn’t installed well or checked regularly. The valves offered by dealers like ALB Industrial Supplies may be made to spec, but someone still needs to check whether or not the valve is doing its job.

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