Did you know you can improve machine efficiency without reducing productivity by selecting pneumatic valves and pressure regulators strategically? Many times, the compressed air delivered to a work point is at a higher pressure than required.
The key to reducing compressed air consumption is reducing the pressure supplied to the machine without affecting force and torque. How can you accomplish such seemingly contradictory goals?
Part I described two different approaches to improving machine efficiency through the strategic selection of pneumatic valves and pressure regulators.Part II will examine four additional ways to reduce compressed air consumption.
If the pneumatic pressure an application requires exceeds a plant’s air supply, the reciprocating booster can be an economical choice. They can be air-to-air or air-to-oil types and single or dual pressure. Single delivers compressed fluid from the intensifier, while dual first delivers pressure from the mains system that then pressurizes the higher-pressure fluid from the intensifier.
Regardless of the selection, here are some ground rules for intensifier use:
Intensifiers operate faster when:
input pressure is adequate;
ports and piping are not oversized - oversized pipes increase the volume to be compressed; and
the intensifier's draining cylinder is pre-exhausted, and the driven cylinder is at line pressure before the power stroke happens.
Bypass the intensifier with a pre-fill low-pressure line by direct connection through a check valve to the pressure vessel and similarly to a dual pressure intensifier.
Regulate the driving pressure to the intensifier to achieve the required high-pressure output.
Keep all piping lengths short. Group the tanks, intensifier, and pressure vessel closely.
An intensifier provides faster cylinder action. It does not need to switch from low to high pressure; it provides high pressure immediately.
Use intensifiers in circuits where there is a need for limited quantities of high-pressure fluid.
A dual pressure circuit, shown in the figure opposite, relies on the fact that many 5-ported, 4-way valves may be employed with dual pressure supplies that enter one end of the cylinder at a high pressure and the other with a lower pressure. The lower pneumatic pressure portions save energy and increase efficiency.
This cylinder, then, extends with a high pressure and retracts with a low one. Here, a dual pressure, solenoid controlled, pilot operated, spring centered, 3-position, 5-ported, 4-way valve, with a blocked center directional valve, has high pressure at port 5 and low pressure at port 3. Port 1 is the common exhaust.
As a solenoid valve is energized, pilot air pressure shifts from the main valve spool to connect ports 5 and 4, which extends the cylinder at a high pressure. As the solenoid is de-energized, this causes the opposite return spring to center the valve.
As the solenoid is energized, it directs the pilot pressure into the valve spool and shifts it such that ports 3 and 2 connect. Thus, the cylinder retracts with low pressure.
This setup, known as energy saving circuits, ensures high-pressure extensions, but low-pressure retractions. This saves operating costs.
Air-to-air booster circuits have a double-acting air-to-air booster, a high-pressure receiver, and a cycling circuit. These are demand-type circuits; they help increase machine efficiency because they run only to raise the receiver pressure up to what is desired. They are controlled by a regulator. A control valve cycles the booster, and it is controlled by the limit valves.
Using air-to-air booster circuits, booster motion continues until a balancing force occurs. After that, reciprocation is determined by system leakage. In such systems, the cam-operated valves should be snap-acting or the intensifier should transverse rapidly.
If an application requires variable motor torque, a torque control circuit can be used. Because the torque is dependent on the pressure at the motor’s inlet, while the speed (in rpm) is dependent on the CFM (dm3/sec), adjusting these can adjust torque.
A circuit can ensure that bi-directional motor torque is different in clockwise and counterclockwise operation. To do so, two secondary regulators, placed between solenoid controlled, pilot operated, 3-position, 5-ported, 4-way, blocked center directional valve and the motor, accomplish this. They must have reverse flow capability; if they do not, then a check valve should bypass the regulator when in reverse flow mode.
To solve the problem of reversing flow through a regulator, use the same components, but the secondary regulators should connect to the 5 and 3 ports on the directional valve. Thus, the same torque is achievable by converting the directional valve into a dual pressure supply valve.
However, what if the situation required torque to vary as the motor turns in one direction or the other? Using an electro-pneumatic regulator, also called a SOR, this is achievable as multiple pressures mean multiple torques.
Which solution will prove best for your machine efficiency goals? That requires calculations and design work, but the options outlined here offer a solid starting point.
Article contributed by Bill Service, marketing manager, Pneumatic Division, Parker Hannifin Corporation.
Much of this content was first published as a Parker Hannifin contribution in Hydraulics and Pneumatics as “Simple Circuits Provide Big Benefits”