Pneumatics 101

VALVE RESPONSE TIME = M + (F x V)

The formula measures time in milliseconds (1 millisecond = .001 second) required to fill the volume, V, to 90 percent of supply pressure or to exhaust the volume, V, to 10 percent of supply pressure. M and F are average response constants, and their values for each valve are found in the ROSS Master Catalog. V is the number of cubic inches in the volume to be filled or exhausted.

M

When the valve is energized, it takes a number of milliseconds for the valve to shift and allow a steady flow of air to be established at the outlet port. Similarly, when the valve is de-energized, it takes a number of milliseconds for the valve to shift and cut off the flow of outlet air and establish the flow of exhaust air. These valve movement times are represented by the M in the formula.

F

After the valve has shifted and air flow to fill the volume V is established, the air flows rapidly at first, then flows at a reducing rate as pressure builds up in the volume V. In exhausting the volume V, air flows rapidly first, then at a reducing rate as pressure falls in V. In either case, the average flow is represented by the "F" in the formula. It is the average number of milliseconds required to fill or exhaust one cubic inch of volume V.

Therefore, the quantity (F x V) is the number of milliseconds needed to fill or exhaust an entire volume V after the valve has shifted.

M and F values are determined from data obtained by response testing. During a response test, time is measured in milliseconds from the application of an input signal to when the valve output pressure reaches 90 percent of its total change. For example, a 3/2 Normally Closed valve has two response times to measure - pressurizing (port 1 to 2) and exhausting (port 2 to 3). With a 100 psig supply, both the pressurizing response (output pressure changes from 0 psig to 90 psig) and the exhausting response (output pressure changes from 100 psig to 10 psig) are measured.

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