Developing a Pneumatic Actuating System to Illustrate the Functioning of an AND Logic Valve
Daniela Voicu1, Radu Vilău2, Ramona-Monica Stoica3
Within the actuation scheme, between the source of energy and the motor, either pneumatic or hydraulic, there are placed different elements, for the distribution, adjustment or control of the system, with the role to ensure the distribution of liquid for the actuation cyclogram and the flow adjustment (changes in actuation speed) and pressure (control of force and torque). In addition to those devices, there are also used auxiliary equipments, to filter, purge, cool-heat the fluid, lubricate etc. In real conditions, almost 30% of the equipment within an actuation system is safety devices, used to protect the personnel or to prevent from performing activities which may endanger him. There are two different approaches, meaning that the European legislation prevents dangerous activities for the personnel through the use of safety equipments and the American legislation imposes a better training of the operator. One way to solve the issue of probable dangerous activities, is to equip the system with AND logic valves, which imply the simultaneous actuation of two or multiple circuits by the operator. In electric actuation, an equivalent of AND logic valves might be the series connection of two normally-open contacts (NO- normal open) (Costache, 1985; Vilău, 2014; Research report CR-1485 / 25.09.2019, “Ferdinand I” Military Technical Academy, 2019) . The use of an AND logic valve implies two simultaneous commands, the same way as the usage of three or four will lead to a compulsory actuation of all, respectively. For example, in case of cupping press, there can be used two manual commands, or even three: two actuated by hand, one by foot, leading up to five simultaneous commands in case of high risk activities: 2 actuated by hand, 2 by foot and 1under its proper weight.
It was designed the following pneumatic model, in order to highlight the functioning of an AND logic valve (FluidSim 5 software documentation; Research report CR- 1543 / 17.12.2019, “Ferdinand I” Military Technical Academy):
The pneumatic model comprises of:
As an example, AND logic valve is used to actuate a press, where, for safety reasons and protection of the personnel, one must have both hands on the actuation device.
1 – air preparation unit;
2 - flow divisor;
3,4 – normally open 3/2 way valve, actuated by push button and spring based extension;
5 – AND logic valve;
6 - single acting cylinder with unilateral rod.
Another application of an AND logic valve is using pressure within a system, from two separate circuits. As an example, it is presented the following pneumatic model:
The pneumatic model comprises of:
Functioning mechanism: when the air compressor starts, both circuits are pressurized because both pistons are at the end of stroke [1,3,6].
After actuating the first pneumatic valve, the compressed air is sent to the first cylinder, which will result in a displacement of the piston, towards the head end of the cylinder (extension stroke).
The air, directed towards the pneumatic valve, was compressed by the piston displacement, leading to an increase of pressure after the AND logic valve. Still, the logic valve will not open unless the second piston reaches the end of stroke, so that the pressure after the valve is equal to the one from the first circuit. Hence, after actuating the second pneumatic valve, it is obtained an equalized pressure between the two circuits, leading to the opening of AND logic valve, and the functioning of the single actuated cylinder [2,3,7].
2,3- 5/2 normally open way valve;
4- AND logic valve;
5,6- double acting cylinder with unilateral rod;
single acting cylinder with unilateral rod;
The proposed applications highlighted the safety aspects regarding the usage of AND logic valves. In addition, one actuation can be determined by ensuring certain pressures on circuits (role of sequence valve). The presented schemes are independent of electric circuits, thus avoiding any interruptions during the actuation process, due to the stop of the electric source. For such situations, there can be used alternative air compressed sources, to ensure a small number of actuations.
*** (2019). Research report CR- 1543 / 17.12.2019, “Ferdinand I” Military Technical Academy.
*** (2019). Research report CR-1485 / 25.09.2019, “Ferdinand I” Military Technical Academy.
*** (2020). Raport de cercetare CR- 1565/ 24.11.2020, Academia Tehnică Militară ”Ferdinand I”
Costache, D. (1985). Hydraulic and pneumatic drives for motor vehicles. Bucharest: Military Academy Publishing House.
*** FluidSim 5 software documentation.
Vilău, R. (2014). Hydraulic and pneumatic drives. Course support.
1PhD Eng., “Dunărea de Jos” University of Galati, Romania, Address: 47 Domneasca Street, Galati, Romania, E-mail: firstname.lastname@example.org.
2PhD Eng., Military Technical Academy “Ferdinand I”, Bucharest, Romania, Address: Blvd. George Cosbuc 39-49, Bucharest 050141, E-mail: email@example.com.
3PhD Eng., Military Technical Academy “Ferdinand I”, Bucharest, Romania, Address: Blvd. George Cosbuc 39-49, Bucharest 050141, Corresponding author: firstname.lastname@example.org.
AUDOE, Vol. 17, No. 6/2021, pp. 270-277