The U.S. Department of Energy estimates that a typical industrial facility uses about 10 percent of its electricity consumption on air compression, making compressed air a major expense in the U.S. Loss of pressure represents money lost. Inefficient systems in production reduce profits and can even threaten the ongoing financial viability of businesses. With such intense price competition, manufacturers can’t afford to overlook unintended costs.
At industrial facilities, untold sums of overhead are consumed by errors in the system, which cause reductions in air pressure between the compressor and the corresponding arsenal of pneumatic devices. The phenomenon is known as pressure drop, which weakens the power of pressurized air supplies and renders applications less efficient. So what is air compressor pressure drop, and how can you minimize the problem?
What Is Air Compressor Pressure Drop?
Pressure drop is a phrase that refers to the instances when pressure loss occurs inside a compressed air system. This can happen at numerous points between the air tank and end-point tools if anything stands in the way to inhibit the flow of pressurized air. Though it’s not possible to eliminate entirely, the problem should only account for a tiny fraction of your machine’s discharge pressure.
If instances of pressure drop proliferate in your system, you will inevitably see a drop in quality from the air-powered tools in your arsenal. When restrictions of flow take root, it takes increased amounts of energy to overcome the problem. If your system cannot yield sufficient air pressure under its normal operating power, the machine will strain itself just to compensate. It is therefore crucial to minimize these issues by any means possible to keep your operations efficient and productive.
When pressure drop occurs, the problem is usually rooted in the after-cooler, check valves or lube separators. Each time the air compressor insists on more discharge pressure, more energy goes to waste. Moreover, increased pressure consumption results in further wasteful usage in other areas.
If you need more pressure at the end-point, make it your first priority to minimize pressure drop. Try to resist the urge to raise the machine’s capacity or boost pressure within the system. If you suppress the regulators to compensate for lost pressure, the regulators will become less responsive when needed in other areas, such as when leaks occur.
What Causes Air Pressure Drop?
Before you can learn how to stop pressure drop, you need to first understand what causes it. So, what’s the cause of pressure drop in air compressors?
So, why does my compressor not build up pressure?Pressure is a measure of force per unit of area.As such, pressurization occurs when high volumes of air are compacted into a short, tight space. In order for this to happen, the air must first be sucked into a chamber for the pressurization to take place. The force imposed on this air must be enforced from all sides with no chance of escape. Without this all-enclosing force, you will not be able to achieve the pressurization needed to turn this supply of air into a power source for tools and machinery.
In an air compressor, the enclosing forces that cause the pressurization of each incoming air supply are created by the walls of the internal chambers. In a rotary screw air compressor, these chambers house counter-rotating helical screws that squeeze the moisture from the air. In a reciprocating air compressor, these chambers house pistons that compact the air into a form of power.
The process will gradually lose its pressurization capabilities if the walls that contain the air lose their structural strength. If cracks or splits, however faint, start to form along these walls, each incoming air supply could be rendered less and less powerful by the time it passes to the end-point application. Basically, the integrity of the chamber that traps each incoming air supply is just as responsible for the power of the outgoing air as the screws and pistons that make the pressurization process possible.
The air that undergoes pressurization inside a compressor is referred to in scientific parlance as gas. While any form of matter that is neither liquid nor solid is technically referred to as gas, the gas compressed within an air compressor is actually ambient air from the machine’s surrounding environment.
To amass the amount of force and intensity required for pressurization, the process needs energy. Air compressors are designed to move energy from a central pressurization chamber to an end-point application, such as a pneumatic brush or sander. The energy put forth by a reciprocating or rotary screw air compressor is intended for use in a linked, adjacent area, where the air is ultimately released at the tip of a tool or within the process of an air-powered machine.
Pressure drop is an unintended consequence of the processes that turns ambient air into pressurized power. Even though pressure drop is undesired, it is inevitable to some degree in virtually any system. Pressure drop comes in two basic varieties: natural and unintended. The natural type of pressure drop is the small amount that will occur, regardless of the tightness and perfection of your system. Unintended pressure drop is the kind that results from flaws within your system that could possibly be rectified if you know how to pinpoint the source of the problem.
When unintended pressure drops occur within a compressed-air system, the problem is typically due to design issues within the distribution network. In physics, pressure is defined as a mechanical property. In many different scenarios, the problem will result from oversight on the part of warehouse managers. If the engineer in charge of planning fails to properly align and place the components of an air system, significant volumes of force could ultimately be lost by the time the pressurized air reaches the corresponding pneumatic tools.
If the system is designed to send air to several different areas across a factory floor, poor planning could result in certain areas receiving insufficient airpower for the tools and processes at hand. In many cases, poor system planning results from hastily laid out system components and rushed purchasing choices.
In if you have the most technically perfect and properly arranged compressed-air system possible, there will inevitably be a certain degree of pressure loss.The Department of Energy advises that a properly designed system should have a pressure loss of much less than 10 percent from the compressor’s discharge to the point of use.However, you can never expect the issue of pressure drop to disappear entirely.
Pressure drop is liable to occur when you add more pipes to a compressed air system. This is due to the fact that pressurization results from air being squeezed into compact spaces. Once the air is passed to a larger area, some of the air pressure is lost.
When you add space for the pressurized air to occupy, you are essentially adding volume to that space itself. The more volume you allow for the air in a pressurized air system, the more pressure you need to retain the power of the compressed air. By adding more pipes to your system, you are increasing the number of avenues for the air to travel, hence reduced pressure. To avoid this pressure loss, you would need to have more pressure to account for the enlarged space. Otherwise, you are taking a supply of air that received x-amount of pressurization in a y-sized space and releasing it to a larger area.
To achieve sufficient airpower for all the applications across your work area, you need to proportion the pressure and volume. This requires you to calculate the level of pressure required for every system tool on the floor of your factory or warehouse. You will not arrive at an accurate calculation if you merely add up all the usage expectations of the various applications because that would fail to take into account the potential for pressure drop along each path.
Air Compressor Blockages
One of the leading causes of pressure drop is any sort of physical obstruction along an air system. When an obstruction is present, it will cause a partial blockage of airflow at the affected point along the system. The blockage might only inhibit a small part of the overall flow, but this can still result in major pressure loss. Obstructions rarely cause complete stops in airflow; if such was the case, the system would quickly shut itself down due to pressure buildup.
Pressure will actually intensify in front of an obstruction and then drop significantly as the air passes the point in question. When you investigate the root of such a problem, this spot of intensity can make it easy to pinpoint the obstruction.
Obstructions are sometimes unintentionally built into a system. If your pipes and connectors are fastened to walls, there might be metal bolts that partially intrude into some of these pipes. Even if the metal barely penetrates the interior of the pipe, it will still reduce the diameter at the point of the air system.
Obstructions can also be caused by valves in an air system. As the air passes through a valve and makes a turn, there will inevitably be a slight change in pressure due to the interruption of flow momentum. Some of the equipment that you might use to monitor your system could also cause reductions in air pressure. Examples include inline sensors and gauges, which can affect air pressure merely by making contact with the pipes and connectors.
The amount of pressure drop that results from these built-in elements is hard to eliminate from the equation. Fortunately, any loss of pressure caused by sensors, valves or fasteners is unlikely to be a major source of inefficiency. Like most compressor operators, you probably have never been aware of the minor impact that these in-built system parts can have on the flow rate of your system.
The one system part that gradually loses its ability to do its intended job is the filter. While filters are put in place to block out particulates that could contaminate pressurized air and impeded its flow, the filters eventually become clogged with dust and dirt. Once the filters become too dirty, the inlet valves draw less and less air into the compressor, thus robbing your system of new air to pressurize. Granted, clean filters can also account for small amounts of resistance, but dirty filters will gradually impede the process of your air compressor.
Pressure Drop Caused by Actual Pressure Drops
Production managers operating inefficient compressed air systems are subjected to their own forms of pressure — time and cost constraints. Every one PSI of excess operating pressure increases air compressor power consumption by about 0.5 percent. So, taking emergency measures without examining your current layout will just worsen cost and output performance.
A pressure drop inhibits the volume of air power that arrives at a given end-point application. When this happens, productions slow and operating costs increase. When managers get wind of these situations, a common reaction is to simply turn up the power to intensify the pressure that reaches each pneumatic application. Such an action could be a hasty error in judgment that would only drive up your costs even further and ultimately lead to system damage and a premature need for costly new parts.
When you overload a system with excessive volumes of pressure, the effects could be damaging and possibly disastrous, especially if you allow the situation to continue unchecked for a period of time. Excessive pressure loads are most damaging to the connecting points in a compressed air system, such as the valves and contacts.
For example, if too much air pressure is forced into a pipe, the pressure could over-stress the connecting point where the pipe begins and result in air leaks. As the overload persists and the component gets even weaker, the pressure could ultimately cause a rupture and render the parts unusable.
Blowing components results in leaks. You probably think that leaks caused your pressure drop. They probably didn’t. Inappropriate pipe gauges, overextended pipe runs, bends, pipe interior irregularities, blockages and dirty filters probably did that. The leaks resulted from overloading, which was a reaction to an unacceptable pressure drop. If you only hunt for leaks, you are looking for the symptoms of your compressed air system problems, not the cause. Detecting leaks will provide evidence of failure. Get them replaced, but then move on to plan a long-term, cost-effective solution to your pressure drop headaches.
When you’re under pressure, you make mistakes. So the first solution to unexpected pressure drops in your compressed air system is to keep calm and commit to yourself that you will not crank up the compressor’s pressure setting until you have fully investigated the cause of the problem. Increasing the force in your system will just introduce leaks and make matters worse.
There are several ways to fix an air compressor pressure drop or loss. Consider a timed approach to resolving the overall issue:
Short Term: Check all the seals and connectors in your system for leakages. Clean or replace all filters and turn down the pressure set points on your compressors.
Medium Term: Place pressure monitors at various points of your system, particularly before and after each device. Check for unusual drops in pressure in the system. Institute regular maintenance checks.
Long Term: Draw out a plan of your system and reorganize the shop floor to reduce pipeline runs. Eradicate all bends and replace pipes that demonstrate unreasonable pressure drops.
Above all, you should realize that your pressure drops cost money, and getting on top of this problem can turn your company around. Lost money through excessive power usage is just going to make your production uncompetitive. Getting the most efficient compressed air system working for you will enable you to increase efficiency to outperform your competitors, putting you ahead of the pack.
How to Calculate Pressure Drop
What is pressure drop calculation?The standard compressed air pressure drop equation for calculating the likely pressure difference between the compressor and the user is known as the “empirical formula.” This formula is:
dp = 7.57 q1.85L 104 / (d5p)
The factors represented by the letters in that formula are as follows:
dp: The drop in pressure, measured in kg/cm2.
q: The volume flow of air, measured in m3/min.
L: The pipe length, measured in meters (m).
d: The diameter of the inside of the pipe, measured in millimeters (mm).
p: The total starting pressure, measured in (kg/cm2).
Despite the math behind this formula, a lot of warehouse managers are put off by its complexities. Consequently, the common practice is to crank the pressure on an air compressor and wait for the pneumatic tools to receive the proper intensities of air pressure. Therein lays the problem that has rendered so many factory operations inefficient when it comes to energy use; when you turn up the pressure to compensate for the loss, you increase the pressure drop and consume excessive amounts of energy. Thus, factory operations become costlier and less productive.
Despite its apparent surface complications, the mathematical formula for calculating pressure drop is based on simple compressor-to-pipe arrangements. The formula does not take into account the possibility of bends along the piping of a compressor system. Another factor that the formula does not take into consideration is the possibility of flow reduction within an air pipe. The interior surface of a tube and the way that the pipe is laid across an air system can both be causes of turbulence during air-powered operations.
Compressor operators often assume that air always travels in a forward direction within the attached pipes, but this is sometimes not the case. Across the layout of air pipes in a system, energy can go to waste as the flow of air is interrupted or set astray by bends and kinks in the piping. At each point along the system where air is misdirected, energy is consumed by these unproductive movements. If the bends are small and elusive to the naked eye, it can be hard to measure the directional flow in a compressed air system.
Whether the air flows in a straight line or not is determined by a factor called the Reynolds number. That factor is derived through the formula:
Re = ρvd/μ
The meanings of these symbols are as follows:
Re: The Reynolds number
ρ: The density of the air
v: The mean of the velocity
d: The pipe diameter
μ: The dynamic viscosity
Once you have the Reynolds number, you are then able to decide whether your air flow is efficient. Air flowing in a straight line is called “laminar flow.” When air is following a convoluted path, it is in a “turbulent flow.” You can label your flow as laminar if your observations resulted in a number lower than 2,300. If it’s higher than 3000, you have turbulent flow.
You might decide to skip the effort of calculating the Reynolds number and just turn up the compressor. This is a common mistake and introduces much greater inefficiency into your power usage. This is because turbulence creates resistance in the flow. Resistance slows down the flow rate and causes a drop in pressure.
You probably think that increasing the pressure in your piping system will ram through the air at a faster speed and overwhelm turbulence. The opposite is true. Higher pressure actually increases turbulence, so overcoming the problem by brute force is not a viable option.