Ross Controls SERPAR AND CROSSFLOW DOUBLE VALVES SERIES 35 - Manual (Page 18)

18 ROSS CONTROLS ®
VALVE RESPONSE TIMES
Most pneumatic applications call for a valve to be used to control
the repeated filling and exhausting device (cylinder, clutch, etc.)
having a certain volume. The time required to fill or exhaust this
volume is called the “valve response time.”
The time to fill a volume is usually different from the time to
exhaust the volume. However, both times can be found using
the following formula:
Valve Response Time (msec) = M + F • V
This formula will give the number of milliseconds (msec) required
to fill the volume V to 90 percent of supply pressure or to
exhaust the volume to 10 percent of supply pressure. M and
F are average response constants, and their values for each
valve are given on the valve specification pages (6-12). V is the
number of cubic inches in the volume to be filled or exhausted.
Response times will be valid for any supply pressure from 3.5
to 8.5 bar (50 to 125 psig).
What is the constant M? When a 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. In a like manner,
when the valve is deenergized, it takes a number of milliseconds
for the valve to cut off the flow of air and establish the flow of
exhaust air. These valve “movement” times are designated by
M in the above formula.
What is the constant F? After the valve has shifted and air
flow (either to fill or exhaust) is established, the air flows rapidly
at first, then flows at a reducing rate. The average flow rate is
represented in the above formula by the letter F. It is the average
number of milliseconds required to fill or exhaust one cubic inch
of the volume V. The product F • V, then, is the average number
of milliseconds required to fill or exhaust the entire volume V
after the valve has shifted.
SAMPLE PROBLEM.
How long will it take to fill a 100-cubic-inch clutch to 90 percent
of supply pressure using a nominal size 8 double valve with
3/4 ports?
Solution. Specifications for size 8 valves are given on pages 8,
10, and 12. From the chart on page 8 (pages 10 and 12 will give
the same values) we find that the average response constants
for a size 8 valve with 3/4 ports are M = 15 and F = 0.65. The
F value of 0.23 is for the exhausting paths and is not needed
for this problem. Putting the M and F values into the response
time formula gives:
Average response time = 15 + (0.65)(100)
= 15 + 65
= 80 msec
Therefore, the 100-cubic-inch volume would be filled to 90
percent of supply pressure in just 80 milliseconds.
AVERAGE C
V
RATINGS
Because widely differing test standards are used in the
measurement of C
V
values, the following figures should not
be used in comparing ROSS valves with other makes. These
C
V
ratings are intended only for use with performance charts
published by ROSS.
THREAD OPTIONS
To serve customers around the world, ROSS supplies double
valves with threaded pressure ports and electrical openings
that conform to various local standards. These variations are
identified by a letter preceding the valve model number or flange
kit number. The specifications for these prefix letters are shown
in the chart at the right.
None
D
J
NPT
DIN 259
(parallel)
DIN 259
(parallel)
1/2 NPSC
R 1/2
R 1/2
3/4 NPSC
R 3/4
R 3/4
Electrical Opening
Prefix
Letter
Pneumatic
Port
Threads
L-G or E-P
Monitor
D-S
Monitor
General Information
4
8
12
30
3/8
1/2
3/4
1/2
3/4
1
3/4
1
11/4
11/4
11/2
3.0
3.0
3.0
3.5
4.0
4.0
8.0
8.5
9.0
20
21
7
9
11
10
14
14
15
19
21
42
43
Average C
V
Ratings
Nominal
Size
Port
Size
1 to 2 2 to 3