The Ton used in British proof was 2240lbs. Thus tons x 2240 is a direct conversion from tons to pounds. What is "NOT" a direct conversion is crusher pressures to piezo-electric pressures which are considered to give true PSI. In the early days of working with the piezo-electric pressures bbls were set up with both P-E & crusher gages & simultaneous readings taken at the same 1.0" station. A "Workable" formula for conversion, within the normal pressure range of shotgun bbls was found to be;
P-E (tons) = (Crusher tons x 1.5)-.5 Multiplying this figure by 2240 will then give psi. Note that this formula was not given to be "Exact" but to give reasonable working pressures. By working through the pressures given per the Birmingham proof house & comparing the greatest difference will be found to be on the order of 3% & this on the 4ton pressure, the other 3 being from 2% down to near zero. The reason for the differences & why no exact formula can be given is because of the varible "Lag Time" in crushing the piston. Within this range crusher pressures will always read less than the P-E pressures.
