Experiment 001 - Increasing the speed in a Double-Acting Cylinder with a 3/2

Quick-exhaust Valve

Equipment Required:

  • Double-acting cylinder.
  • 5/2-way with selector switch.
  • 3/2-way quick-exhaust valve.
  • T-connectors

Discussion:

In this experiment, we will learn the work of a quick-exhaust valve. This valve is also well-known as flow selector.

Quick exhaust valves (QEV) increase cylinder rod speed by dumping exhaust air directly at the cylinder instead of back through the control valve. Use one QEV in each cylinder port to increase rod speed in both directions.

Using a quick exhaust valve to increase cycling speed allows a smaller, less expensive control valve to be used

Quick Exhaust Valves are used with Air Cylinders, Brakes, Clutches, etc. to speed their reaction or travel time by exhausting the air directly to atmosphere rather than back through a restrictive control valve

Figure 001-1 Quick-exhaust valve

Mode of Operation: The air that enters by feeding port (P) moves the clogging membrane, which blocks the exhaust (R) and connects the port (A) so that a certain work device fills. When the feeding stops in (P), the under pressure accumulated air moves the membrane towards (P) and escapes quickly by (R).

Figure 001-2 Increasing the speed in a Double-Acting Cylinder

using a 3/2 Quick-Exhaust Valve

Preparation Questions:

1)For the QEV, which of the following is the correct statement?

a)It is a control component.

b)It is the same as a shut-of valve.

c)It is a work component.

d)It works under low pressure only.

2)Why a QEV is installed in the ports of a double-acting cylinder?

a)To increase the cylinder rod speed in one direction.

b)To obtain the maximum speed of the cylinders.

c)To quickly vent exhaust air at the cylinder ports rather than porting the exhaust all the way back through the valve.

d)To increase the time-delay of the cylinder

3)How the speed increasing of the cylinder is performed?

a)By the increase of the inlet pressure.

b)By the greater diameter of the outlet orifice of the exhaust port.

c)By the decrease of the outlet pressure.

d)By providing immediate outlet to atmosphere of the exhaust air.

4)Sign the correct statement:

a)The increase of the rod speed in both directions in a cylinder can be obtained with the application of a single QEV.

b)QEV are used only with air cylinders.

c)When pressure is removed from input port P back flow at port 2 unseats the poppet and allows flow through exhaust port 3.

d)None of the previous ones.

Question / Answer
1 / a
2 / b
3 / d
4 / c

Procedure:

Step 1:Adjust the air pressure on the air supply regulator to 2 ATM pressure.

Step 2:Implement the circuit depicted in figure 001-2 and try to understand its operation.

Step 3:Checking out the 3/2 quick-exhaust valve (QEV):

a) Locate the inlet and outlet ports and the activation port of the valve according the mode of operation paragraph.

b) The valve should be mounted as closer as possible to the cylinder’s connection port.

Step 4:Assembling the control circuit.

a)Connect one outlet port of the valve to the inlet port of the cylinder (B+).

b)Connect the other outlet port of the valve to the inlet port (P) of the QEV, as is showing in the figure.

c)Connect the outlet port (A) of the QEV to the second inlet port of the cylinder (B-).

d)Connect the inlet port of the valve to the air supply.

e)Adjust the FCV (Flow Control Valve) to maximum open position.

Step 5:Operate the control circuit:

a)Operate the circuit a few times and describe what happened with the QEV.

b)Change the outlet port (A) position in the cylinder with the other.

c)Operate the circuit a few times and describe what happened with the QEV.

Final Questions:

1)Besides the increase of the speed of the cylinder, what another effect is more evident in the experiment?

a)There is no relevant effect.

b)A small noise and the fast exhaust of the air.

c)There is no air exhaust by the 5/2-way valve.

d)None of the previous ones.

2)Sign the correct statement:

a)The directional control valve in any power circuit should be mounted as close as possible to the cylinder it controls.

b)Pressure drops in long hoses leading to the cylinder may cause the piston to move too fast.

c)In a quick-exhaust valve, the resulting decrease in back pressure causes the cylinder to travel much slower.

d)None of the previous ones.

3)Sign the false statement:

a)QEV makes it possible to achieve increased piston speeds on the exhaust stroke with single acting and double acting cylinders.

b)QEV is a speed control valve with flow exhaust.

c)QEV makes it possible to achieve increased piston speeds on the exhaust stroke with double acting cylinders only.

d)None of the previous ones.

Question / Answer
1 / b
2 / a
3 / c

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