Title: Air Filter / Pressure Drop
Course: Fluid Power Pneumatics (Sandbox) > Section: Module 4: Breaking Down a Pneumatic System / Air Delivery Side - 10 Hours

Shutoff Valve and Filter

Now that we have gone over compressors and we understand that a compressor is what supplies a pneumatic system with the air that it needs to do work, let's continue following the schematic. The next couple of components that we come to are a shutoff valve and a filter.

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

A shutoff valve is put into a system so that all air going to that system can be shut off. This is helpful, because in a manufacturing facility where there are many machines near each other, each one can be shut off individually without affecting other machines. Being able to shut off all incoming air to a certain pneumatic system allows for maintenance technicians to perform "Preventative Maintenance" tasks on that machine safely.

Next, as we follow along, we come to a filter. The compressed air we use in pneumatics comes from the atmosphere. That means that our air supply contains dust, pollution, and other small particles which are too small to see. Components, such as cylinders and valves, have close fitting parts which must slide back and forth. However, dirt will keep these parts from working smoothly.

An air filter is a device designed to clean the air before it enters the pneumatic system. It will also remove water droplets from the air supply but not water vapor. All pneumatic systems should be installed with one or more air filters. The following is a cut away and the schematic symbol for an air filter.

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

The only moving item in an air filter is the air itself. The air coming into the filter hits a deflector. The deflector makes the air spin around the inside of the filter bowl. This spinning action "throws" the heavier particles against the sides of the bowl where they drop past the baffle to the bottom. The air then swirls into the filter element. The smaller particles are trapped in the filter element and the clean air passes through the outlet connection. Water that has collected in the filter bowl must be drained before the level reaches the bottom of the baffle.

Some pneumatic systems have filters that are integrated with the pressure regulator. The pressure regulator is the next component that we will talk about. These integrated regulators and filters are commonly called "FR Units", which stands for filter/regulators.

The following is a picture of the "FR" unit that we will use on our trainer. As you can see, the part of the "FR" unit that is circled in yellow is the regulator part of the FR unit. The part of the FR unit that is circled in black is the filter part of the unit. Here is the schematic symbol for an "FR" unit.  The dashed box indicates the different components that make up an "FR" unit:

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

As we can see, air must pass through the FR unit. As it passes through the FR unit, something called "pressure drop" occurs. Pressure drop happens when air passes through any pneumatic component. Pressure drop is the pressure differential between two points. The main factor that causes pressure drop is the velocity (speed of the air going in a certain direction) of the air going through the component.

Reference the following chart.

Parker Hannifin Corporation. (1980). Industrial Pneumatic Technology. Parker Hannifin Corp. DOI: 1557690154

Look at the 30 psi line on the left side of the chart. As you can see, as the air flow (SCFM, Standard Cubic Feet per Minute) increases, the pressure drop between the inlet and outlet sides. In other words, there is a greater loss of pressure as we try to put a larger volume of air through the same sized component. If you have 30 psi, at 20 SCFM, you can see that you drop 10 psi. At 100 SCFM, you can see that you lose 20 psi. Pressure drop is important when you design systems. If you want less pressure drop, you must increase the size of the component.

We will talk more about flow and pressure drop in the next modules.

Unless specified otherwise, any and all work on this page is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.