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'CATS' Direct Mount (NAMUR)
Directional Control Valves |
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Download 'CATS' Control Valves PDF Brochure
'CATS'
Solenoid Valve
Valve
Automation Center
Only with the 'CATS' Direct Mount Directional
Control Valves can you:
- Prevent atmospheric contamination of Actuator
internals
- Ensure
'Fail Safe' Actuator Springs
do not corrode
"CATS" is the HYTORK® acronym
for "Clean Air To Springs". This principle,
pioneered by Hytork®, is designed to prevent contamination and corrosion
of the internals of Spring Return Chambers. |
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Spring Return
Actuators
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Spring Return Actuators use air power to move in one direction, which
both performs the required operation and also compresses the Springs to
provide stored energy for the return stroke.
It is important to prevent the Spring Chamber becoming pressurised in
the very unlikely event of leaks from the air pressure side. If the
pressure side were to leak into the Spring Chamber the air pressure
would add to the force of the Springs and operate the Actuator in the
Spring direction. To prevent this situation occurring Spring Return
Actuators must have the Spring Chambers vented.
As the Springs operate they push the Pistons together. This movement
increases the volume in the Spring Chambers causing a pressure drop to
below atmospheric pressure. The higher atmospheric pressure now fills
the Chambers and any contaminants in the atmosphere are drawn in via the
vents.
Actuators installed in environments with dusts, sand, chemicals and even
water are vulnerable, as these contaminants can effect the performance
of the Actuators, possibly leading to seizure or corrosion, negating the
choice of a "Fail Safe" Actuator.
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Double
Acting Actuators |
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Double Acting Actuators cannot draw
in dirty air from the atmosphere.
Double Acting Actuators are fitted
with a 5/2 Directional Control Valve with five ports and two spool
positions. One port is for the pressure supply, two ports direct
pressure to the selected Actuator pressure Chambers and the other
two ports open the exhausting Chambers to the atmosphere. In this case
the inside of the Actuator is always sealed from ambient conditions and
is purged with clean instrument air each time the Actuator Operates.
Conventional 3/2 Directional
Control Valves used on Spring Return Actuators cause contaminants to be
drawn into the Spring Chamber.
Traditionally Spring Return Actuators,
which require air power in one direction only, have been fitted with 3/2
Directional Control Valves, as illustrated in Fig. 1.
This is a Valve with three ports and two spool positions. One port is
for air supply, a second port directs this to the Actuator when the
spool is in position "a" and the third port opens the pressure
Chamber to exhaust when the spool is in position "b".
Use of this type of Valve does not purge the Spring Chamber which is
left to draw in air from the surrounding environment. The Actuator
should be protected from this danger.
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Comparison |
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The Hytork®
Solution: the "CATS" Directional Control Valve protects the Actuator
internals from contamination. The "CATS" Directional Control Valve
is designed to solve the problem encountered by Spring Return Actuators
fitted with 3/2 Directional Control Valves. The "CATS" Valve protects
the Actuator internals from contamination by ensuring that the Actuator,
when operating in Spring Return mode, is always supplied with clean
instrument air. |
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How
"CATS" Protects Your Actuator |
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The schematic drawing in fig. 2 shows the
"CATS" Valve fitted to a Spring Return Actuator.
Air Direction (Coil Energised)
When instrument air is supplied to the Actuator the "CATS" Valve acts
just like a conventional 3/2 Valve and the air pushes the Pistons apart
which turns the Actuator Pinion and compresses the Springs.
As the Pistons compress the Springs, the air from the Spring Chambers
exhausts to atmosphere through the "CATS" Valve.
The unique design of the "CATS" Valve now ensures that dirty and
corrosive atmospheric air does not fill this partial vacuum, causing
destructive corrosion and contamination to build up inside the Actuator.
As the Springs push the Pistons together they force the instrument air
from between the Pistons via internal passages inside the "CATS" Valve
to fill the partial vacuum in the Spring Chambers. Once the Spring
Chambers are full with this CLEAN INSTRUMENT AIR the remaining
instrument air exhausts into the atmosphere.
This action does NOT pressurise the Spring Chambers. It just prevents
the potentially dirty atmospheric air being drawn into the Actuator.
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