To understand the value of a having a Pressure Regulator at every point of use we should start with identifying the two types of Pressure Regulators, Direct Acting & Pilot Operated. Direct Acting are the least expensive and most common (as shown above), however they may provide less control over the outlet pressure, especially if they are not sized properly. However when sized properly they do an outstanding job. Pilot Operated Regulators incorporate a smaller auxiliary regulator to supply the required system pressure to a large diaphragm located on the main valve that in turn regulates the pressure. The Pilot Operated Regulators are more accurate and more expensive making them less attractive to purchase. The focus of this Blog will be on the Direct Acting Pressure Regulator.
The Direct Acting Pressure Regulator is designed to maintain a constant and steady air pressure downstream to ensure whatever device is attached to it is operated at the minimum pressure required to achieve efficient operation. If the end use is operated without a regulator or at a higher pressure than required, it result’s in increased air demand and energy use. To clarify this point, if you operate your compressed air system at 102 PSI it will cost you 1% more in electric costs than if the system was set to run at 100 PSI! Also noteworthy is that unregulated air demands consume about 1% more flow for every PSI of additional pressure. Higher pressure levels can also increase equipment wear which results in higher maintenance costs and shorter equipment life.
Sizing of the Air Regulator is crucial, if it is too small to deliver the air volume required by the point of use it can cause a pressure drop in that line which is called “droop”. Droop is defined as “the drop in pressure at the outlet of a pressure regulator, when a demand for compressed air occurs”. One commonly used practice is to slightly oversize the pressure regulator to minimize droop. Fortunately we at EXAIR specify the correct sized Air Regulator required to operate our devices so you will not experience the dreaded “droop”!
Another advantage to having a Pressure Regulator at every point of use is the flexibilty of making pressure adjustments to quickly change to varying production requirements. Not every application will require a strong blast sometimes a gentle breeze will accomplish the task. As an example one user of the EXAIR Super Air Knife employs it as an air curtain to prevent product contamination (strong blast) and another to dry different size parts (gentle breeze) coming down their conveyor.
EXAIR products are highly engineered and are so efficient that they can be operated at lower pressures and still provide exceptional performance! This save’s you money considering compressed air on the average cost’s .25 cents per 1000 SCFM.
Compressed air regulators are a pressure reducing valve that are used to maintain a proper downstream pressure for pneumatic systems. There are a variety of styles but the concept is very similar; “maintain a downstream pressure regardless of the variations in flow”. Regulators are very important in protecting downstream pneumatic systems as well as a useful tool in saving compressed air in blow-off applications.
The basic design of a regulator includes a diaphragm, a stem, a poppet valve, an orifice, compression springs and an adjusting screw. I will break down the function of each item as follows:
Diaphragm – it separates the internal air pressure from the ambient pressure. They are typically made of a rubber material so that it can stretch and deflect. They come in two different styles, relieving and non-relieving. Relieving style has a small hole in the diaphragm to allow the downstream pressure to escape to atmosphere when you need to decrease the output pressure. The non-relieving style does not allow this, and they are mainly used for gases that are expensive or dangerous.
Stem – It connects the poppet valve to the diaphragm. This is the “linkage” to move the poppet valve to allow compressed air to pass. As the diaphragm flexes up and down, the stem will close and open the poppet valve.
Poppet valve – it is used to block the orifice inside the regulator. It has a sealing surface to stop the flowing of compressed air during zero-flow conditions. The poppet valve is assisted by a spring to help “squeeze” the seal against the orifice face.
Orifice – it is an opening that determines the maximum amount of air flow that can be supplied by the regulator. The bigger the orifice, the more air that can pass and be supplied to downstream equipment.
Compression springs – they create the forces to balance between zero pressure to maximum downstream pressure. One spring is below the poppet valve to keep it closed and sealed. The other spring sits on top of the diaphragm and is called the adjusting spring. This spring is much larger than the poppet valve spring, and it is the main component to determine the downstream pressure ranges. The higher the spring force, the higher the downstream pressure.
Adjusting screw – it is the mechanism that “squeezes” the adjusting spring. To increase downstream pressure, the adjusting screw decreases the overall length of the adjusting spring. The compression force increases, allowing for the poppet valve to stay open for a higher pressure. It works in the opposite direction to decrease the downstream pressure.
With the above items working together, the regulator is designed to keep the downstream pressure at a constant rate. This constant rate is maintained during zero flow to max flow demands. But, it does have some inefficiencies. One of those issues is called “droop”. Droop is the amount of loss in downstream pressure when air starts flowing through a regulator. At steady state (the downstream system is not requiring any air flow), the regulator will produce the adjusted pressure (If you have a gage on the regulator, it will show you the downstream pressure). Once the regulator starts flowing, the downstream pressure will fall. The amount that it falls is dependent on the size of the orifice inside the regulator and the stem diameter. Charts are created to show the amount of droop at different set pressures and flow ranges (reference chart below). This is very important in sizing the correct regulator. If the regulator is too small, it will affect the performance of the pneumatic system.
The basic ideology on how a regulator works can be explained by the forces created by the springs and the downstream air pressures. The downstream air pressure is acting against the surface area of the diaphragm creating a force. (Force is pressure times area). The adjusting spring force is working against the diaphragm and the spring force under the poppet valve. A simple balanced force equation can be written as:
Fa ≡ Fp + (P2 * SA)
Fa – Adjusting Spring Force
Fp – Poppet Valve Spring Force
P2 – Downstream pressure
SA – Surface Area of diaphragm
If we look at the forces as a vector, the left side of the Equation 1 will indicate a positive force vector. This indicates that the poppet valve is open and compressed air is allowed to pass through the regulator. The right side of Equation 1 will show a negative vector. With a negative force vector, the poppet valve is closed, and the compressed air is unable to pass through the regulator (zero flow).
Let’s start at an initial condition where the force of the adjusting spring is at zero (the adjusting screw is not compressing the spring), the downstream pressure will be zero. Then the equation above will show a value of only Fp. This is a negative force vector and the poppet valve is closed. To increase the downstream pressure, the adjusting screw is turned to compress the adjusting spring. The additional spring force pushes down on the diaphragm. The diaphragm will deflect to push the stem and open the poppet valve. This will allow the compressed air to flow through the regulator. The equation will show a positive force vector: Fa > Fp + (P2 * SA). As the pressure downstream builds, the force under the diaphragm will build, counteracting the force of the adjusting spring. The diaphragm will start to close the poppet valve. When a pneumatic system calls for compressed air, the downstream pressure will begin to drop. The adjusting spring force will become dominant, and it will push the diaphragm again into a positive force vector. The poppet valve will open, allowing the air to flow to the pneumatic device. If we want to decrease the downstream air pressure, the adjusting screw is turned to reduce the adjusting spring force. This now becomes a negative force vector; Fa < Fp + (P2 * SA). The diaphragm will deflect in the opposite direction. This is important for relieving style diaphragms. This deflection will open a small hole in the diaphragm to allow the downstream air pressure to escape until it reaches an equal force vector, Fa = Fp + (P2 * SA). As the pneumatic system operates, the components of the regulator work together to open and close the poppet valve to supply pressurized air downstream.
Compressed air is expensive to make; and for a system that is unregulated, the inefficiencies are much greater, wasting money in your company. For blow-off applications, you can over-use the amount of compressed air required to “do the job”. EXAIR offers a line of regulators to control the amount of compressed air to our products. EXAIR is a leader in manufacturing very efficient products for compressed air use, but in conjunction with a regulator, you will be able to save even more money. Also, to make it easy for you to purchase, EXAIR offer kits with our products which will include a regulator. The regulators are already properly sized to provide the correct amount of compressed air with very little droop. If you need help in finding the correct kit for your blow-off application, an Application Engineer at EXAIR will be able to help you.
In order to fully understand how efficient your compressed air system may be, you will need to generate a system pressure profile at some point. This is a list or diagram of what pressures you have in your compressed air system at specific locations, as well as the pressure required by all the demand devices on your compressed air system.
One of the reasons for the pressure profile is that you may have an application that is far away from the compressor but also highly dependent on a specific operating pressure. You may also find an application that, due to pressure losses within the system, causes an artificially high pressure demand.
The list below gives the critical points for measuring your compressed air system profile.
At the air compressor discharge. (If using multiple compressors, measure at each.)
If dryers of any type are being used after the compressor measure downstream from the dryer.
Downstream of each filter. (If a particulate filter and oil removal filter are being used it is best to measure downstream of each individual device. This is to tell when you have more than a 5 psig pressure drop or a clogged filter.)
At the point just before the main line from your compressor room branches off to distribution.
The furthest point of each header line you have installed.
On both sides of every filter/regulator units that are at high pressure point of use applications.
To give you an idea of why it is so important to measure these locations, take a look at the blogs we have posted on pressure drop. (Link Here) As you can tell by the list of blogs that comes up, pressure drop through piping can really cause a lot of wasted energy in your compressed air system. If you can get a good base line measurement by utilizing a pressure profile then you can start the process to optimizing your compressed air system.
The past several weeks I have been finding myself doing things the more complicated way (I know how that sounds odd – an engineer that prefers to do things the hard way). Over the weekend I took a brief ride on the motorcycle for a short 15 minute trip that I found to be satisfying, even if it is less direct and a more out-of-the-way route for getting my errands complete. The route runs past the local university of Mount Saint Joseph, down a winding road that has no houses and only one business, the rest is all woods and a creek. Finally, this route runs along the mighty Ohio river and back up a steep winding road near my house.
While I have been worrying about all the projects and errands which need to be completed, this more complicated route gives me a moment to decompress and remember that my family at home and few other things are all I need. Once I was reminded of that and got some perspective which allowed me to “keep calm and carry on” I proceeded to break my projects and errands down into smaller pieces and everything will start to come together.
I now have a to do list at home as well as a refreshed list at EXAIR of all the items I need to do. The list at home is considerably more fun as it all involves getting my “new to me” track bike ready for this season. That’s right, it’s right around the corner, the first track weekend of 2014. So expect to see some more motorcycle blogs coming and hopefully more ways to use EXAIR products while working on them. It was these newly developed lists that helped me reorganize and get back on track for the new season, sometimes a list is necessary in order to gain perspective, prioritize and begin to take action.
On that note, EXAIR has a list to help you gain perspective, prioritize and take some action toward getting your compressed air system optimized. Our systematic approach using the Six Steps To Compressed Air Optimization has been developed to help you save your compressed air,your hearing, and your money. By following these steps you can lower your compressed air use, minimize workplace noise exposure (OSHA will be happy) and save money on this important utility.
If you have ever thought of reducing your compressed air costs, use our list to help you gain perspective on this simple process and take some positive steps toward saving your facility some money.