The Basics of Air Compressor Pressure Regulation

Pressure is one of the key factors that determines capacity and power required on a compressed air system.

Having compressed air system designed for a much higher or a lower pressure than the optimum plant pressure requirements results in increased operating costs or additional investment in case of lower pressure to adapt and modify the system.

Pressure regulation is a way to adapt your machine delivering you the required operating pressure value without any comprise on the downstream accessories and avoiding any unnecessary running cost.

The best & the most optimally designed system builds adequate pressure as required by the process and maintains the pressure without much fluctuations.

Different methods to regulate system pressure

There are several flow regulation methods available, depending on the type of compressor, acceptable pressure variations, air consumption variations and acceptable energy losses. Energy consumption represents approximately 80% of the total life cycle cost for compressed air, which means that the choice of a regulation system must be made carefully. This is primarily due to significant differences in performance broadly with regards to compressor types or manufacturers. In an ideal case scenario, the compressor’s full capacity could be precisely matched to its air consumption, for example, by carefully choosing the gearbox’s transmission ratio (as this is something that is frequently used in process applications). Several applications are self-regulating, i.e. Increased pressure creates an increased flow rate, and as a result, stable systems. Examples include pneumatic conveying systems, ice prevention, chilling systems etc. However, in many applications, the flow rate must be regulated. This is usually performed using regulation equipment that is integrated in the compressor. There are three main groups of regulation systems:

1. Modulating control system

This involves an inlet device typically a throttle valve which regulates the flow of air entering the compressor linked to system pressure. If the pressure increases the valve closes partially sending less air into the compression chamber thereby reducing the compressor output and maintaining the pressure within the allocated pressure band. This regulation however is inefficient in part load conditions as the power consumed does not drop proportionally as the flow reduces. Maintains pressure variations between 0.1 to 0.5 barg.

2. Load/unload regulation

It’s the most common regulation method and involves the acceptance of somewhat larger variations in pressure between two limit values. This takes place by completely stopping the flow rate at the higher pressure (off-loading) and resuming the flow rate (loading) when the pressure has dropped to the lowest limit value. Pressure variations depend on the permitted number of load/unload cycles per time unit, but normally lie within the 0.3 to 1 bar range.

3. VSD regulation

This continuous flow rate regulation involves the continuous control of the drive motor (VSD regulation) according to variations in pressure. The result is normally small pressure variations (0.1 to 0.3 bar) and is the most optimum regulation method employed involving fluctuating air demands and installations having only one compressor or in multiple compressor installation one amongst the other fixed speed L/UL compressors.

Benefits of the compressed air pressure regulation

Protecting your application from the unnecessary high pressure air that could damage the downstream instruments, devices, valves etc.
Delivering the required value of the pressure to the application and avoiding any malfunction, downtime or fault in the application due to low pressure air delivery.
Saving compressed air and consequently operating costs as 1 bar higher pressure results in 7% extra energy consumption

Application requires different values of pressure

Some clients have different applications with different pressure requirements operating at same time, selection of the compressors in these situations should be discussed with an Atlas Copco sales engineer. A detailed analysis and study of the different applications and pressures at different points can be done to evaluate and offer an appropriate system that has lowest energy consumption and thereby lowest cost of ownership.

Pressure regulator on Atlas Copco air compressors

pressure-regulator-on-Atlas-Copco-compressor

Atlas Copco service Engineer sets the LOAD, UNLOAD and SETPOINT pressure parameters during the commissioning via On-board controller according to the application pressure requirement. The controller maintains the net pressure between programmable limits by automatically loading and unloading the unit (fixed speed units) or by adapting the motor speed (units with frequency converter). The controller stops the unit whenever possible to reduce the power consumption and restarts it automatically when the net pressure decreases. If the expected unloading period is too short, the unit is kept running to prevent too short standstill periods. On a VSD compressor the fluctuations in pressure are eliminated as pressure is maintained by regulating speed of the motor through the compressor controller based on anticipation of the system pressure increase or decrease. VSD regulation can bring substantial savings by eliminating unloaded operation of the compressor by far.