These valves coincided with a change in firing behaviour. Rather than demonstrating their virility by always showing a feather at the valve, firemen now tried to "avoid" noisy blowing off, especially around stations or under the large roof of a major station. This was mostly at the behest of stationmasters, but firemen also realised that any blowing off through a pop valve wasted several pounds of boiler pressure; estimated at 20 psi lost and 16 lbs or more of shovelled coal.