Receiver Tank Calculations

Receiver Tank

My colleague, Lee Evans, wrote a blog about calculating the size of receiver tanks within a compressor air system.  (You can read it here: Receiver Tank Principle and Calculations).  But, what if you want to use them in remote areas or in emergency cases?  During these situations, the air compressor is not putting any additional compressed air into the tank.  But, we still have potential energy stored inside the tanks similar to a capacitor that has stored voltage in an electrical system.  In this blog, I will show how you can calculate the size of receiver tanks for applications that are remote or for emergency systems.

From Lee Evans’ blog, Equation 1 can be adjusted to remove the input capacity from an air compressor.  This value is Cap below.  During air compressor shutdowns or after being filled and removed, this value becomes zero.

Receiver tank capacity formula (Equation 1)

V = T * (C – Cap) * (Pa) / (P1-P2)

V – Volume of receiver tank (cubic feet)

T – Time interval (minutes)

C – Air requirement of demand (cubic feet per minute)

Cap – Compressor capacity (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Tank pressure (PSIG)

P2 = minimum tank pressure (PSIG)

 

Making Cap = 0, the new equation for this type of receiver tank now becomes Equation 2.

Receiver tank capacity formula (Equation 2)

V = T * C * (Pa) / (P1-P2)

With Equation 2, we can calculate the required volume of a receiver tank after it has been pre-charged.  For example, EXAIR created a special Air Amplifier to remove toxic fumes from an oven.  The Air Amplifier was positioned in the exhaust stack and would only operate during power failures.  In this situation, product was being baked in an oven.  The material had toxic chemicals that had to cross-link to harden.  If the power would go out, then the product in the oven would be discarded, but the toxic fumes had to be removed.  What also doesn’t work during power outages is the air compressor.  So, they needed to have a receiver tank with enough volume to store compressed air.  From the volume of the oven, we calculated that they need the special Air Amplifier to operate for 6 minutes.  The compressed air system was operating at 110 PSIG, and the Air Amplifier required an average air flow of 10 cubic feet per minute from the range of 110 PSIG to 0 PSIG.  We are able to calculate the required receiver volume to ensure that the toxic fumes are evacuated from the oven in Equation 2.

Receiver tank capacity formula (Equation 2)

V = T * C * Pa / (P1 – P2)

V = 6 minutes * 10 cubic feet per minute * 14.7 PSIA / (110 PSIG – 0 PSIG)

V = 8 cubic feet.

Receiver tanks are more commonly sized in gallons.  In converting 8 cubic feet to gallons, we get a 60-Gallon Receiver Tank.  EXAIR recommended the model 9500-60 to be used near the oven to operate the special Air Amplifier during power outage.

Another way to look at Equation 2 is to create a timing equation.  If the volume of the tank is known, we can calculate how long a system will last.  In this example for scuba diving, we can use this information to configure the amount of time that a tank will last.  The diver has a 0.39 cubic feet tank at a pressure of 3,000 PSIG.  I will use a standard Surface Consumption Rate, SCR, at 0.8 cubic feet per minute.  If we stop the test when the tank reaches a pressure of 1,000 PSIG, we can calculate the time by using Equation 3.

Receiver tank timing formula (Equation 3):

T = V * (P1 – P2) / (C * Pa)

T – Time interval (minutes)

V – Volume of receiver tank (cubic feet)

C – Air demand (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Initial tank pressure (PSIG)

P2 – Ending tank pressure (PSIG)

By placing the values in the Equation 3, we can calculate the time to go from 3,000 PSIG to 1,000 PSIG by breathing normal at the surface.

T = 0.39 cubic feet * (3,000 PSIG – 1,000 PSIG) / (0.8 cubic feet per minute * 14.7 PSIA)

T = 66 minutes.

What happens if the diver goes into deeper water?  The atmospheric pressure, Pa, changes.  If the diver goes to 100 feet below the surface, this is roughly 3 atmospheres or (3 * 14.7) = 44.1 PSIA.  If we use the same conditions above except at 100 feet below, the time will change by a third, or in looking at Equation 3:

T = 0.39 cubic feet * (3,000 PSIG – 1,000 PSIG) / (0.8 cubic feet per minute * 44.1 PSIA)

T = 22 minutes. 

If you have any questions about using a receiver tank in your application, you can contact an EXAIR Application Engineer.  We will be happy to solve for the proper volume or time needed for your application.

 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Optimizing Your Current Compressed Air System Is Simple

A few weeks ago, we posted a blog discussing how artificial demand and leaks can lead to poor performance and expensive waste.  Today, I’d like to review how following a few simple steps can help optimize your current compressed air system and reduce compressed air usage.

The first step you want to consider is measuring the air usage in the system. To do this, you want to start at the compressor and check individual leads to each drop point to a blowoff device, record your findings to track the demand. By measuring your compressed air usage, you can locate the source of high usage areas and monitor the usage on each leg of the system. If the demand exceeds the supply, there is potential for problems to arise, such as lowered pressure and force from compressed air operated devices leading to irregular performance.

Digital Flowmeter with wireless capability

EXAIR’s Digital Flowmeters are designed to measure flow continuously and accurately to give you real-time flow measurements of your compressed air system to help identify problems areas.

Step 2 is to locate the source of waste. Again, compressed air leaks can result in a waste of up to 30% of a facility’s compressor output. A compressed air leak detection and repair program can save a facility this wasted air. Implementing such a program can be used as a way for a facility to “find” additional air compressor capacity for new projects. Whenever a leak occurs, it will generate an ultrasonic noise.

Model # 9061 Ultrasonic Leak Detector

Our Ultrasonic Leak Detector is designed to locate the source of ultrasonic sound emissions up to 20’ away. These ultrasonic sound emissions are converted to a range that can be heard by humans. The sound is 32 times lower in frequency than the sound being received, making the inaudible leaks, audible through the included headphones and the LED display gives a visual representation of the leak.

The 3rd step involves finding the source of noisy and wasteful blowoffs, like open pipes or homemade blowoffs, and replacing them with an energy efficient, engineered solution. By replacing these devices, you are not only reducing the amount of waste but also improving operator safety by complying with OSHA safety requirements.

Model # 9104 Digital Sound Level Meter

EXAIR’s Digital Sound Level Meter is an easy to use instrument that measures and monitors the sound level pressure in a wide variety of industrial environments. The source of loud noises can be quickly identified so that corrective measures can be taken to keep sound levels at or below OSHA maximum allowable exposure limits.

The easiest way to reduce compressed air usage and save on operating expense is to turn off the compressed air to a device when it isn’t needed, step 4 in the process. Not only will this save money, in many cases, it can also simplify a process for the operator.

 

Sizes from 1/4″ NPT up to 1-1/4″ NPT are available

A simple manual ball valve and a responsible operator can provide savings at every opportunity to shut down the air flow.

 

120VAC, 240VAC or 24VDC

 

For automated solutions, a solenoid valve can be operated from a machine’s control. For example, if the machine is off, or a conveyor has stopped – close the solenoid valve and save the air.

 

 

Model # 9040 Foot Valve

A foot pedal valve offers a hands free solution to activate an air operated device only when needed, such as being implemented in an operator’s work station.

 

EFC – Electronic Flow Control

For even more control, you can use a device like our EFC or Electronic Flow Control. This helps minimize compressed air usage by incorporating a programmable timing controlled (0.10 seconds to 120 hours) photoelectric sensor to turn off the compressed air supply when there are no parts present. It is suited for NEMA 4 environments and can be easily wired for 100-240VAC.

 

 

Step 5, intermediate storage. Some applications require an intermittent demand for a high volume of compressed air. By installing a receiver tank near the point of high demand, there is an additional supply of compressed air available for a short duration. This will help eliminate fluctuations in pressure and volume.

Model # 9500-60

EXAIR offers a 60 gallon, ASME approved vertical steel tank with mounting feet for easy installation near high demand processes.

Many pneumatic product manufacturers have a certain set of specifications regarding performance at stated input pressures. In many applications, or in the case of using a homemade blowoff device like open pipe, these wouldn’t necessarily require the full rated performance of the device or full line pressure. Controlling the air pressure at the point-of-use device will help to minimize air consumption and waste, step 6.

Pressure Regulators permit easy selection of the operating pressure

By simply installing a pressure regulator on the supply side, you can start off at a low pressure setting and increase the pressure until the desired result is achieved. Not only will this help to conserve energy by only using the amount of air required for the application, it also allows you to fine tune the performance of the point-of-use device to match the application requirements.

If you have any questions, please contact an application engineer at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

Advantages of Thermal Mass or Thermal Dispersion Flow Measurement

EXAIR’s Digital Flow Meter offers an easy way to measure, monitor and record compressed air consumption. The Digital display shows the current amount of compressed air flow, allowing for tracking to identify costly leaks and/or inefficient air users.

dfm

How exactly does the Digital Flow Meter work?  The unit falls under the category of Thermal Mass or Thermal Dispersion type flow meters.  Below shows the backside of a unit.

IMG_7387

Thermal mass flow meters have the advantage of using a simple method of measuring flow without causing a significant pressure drop. The EXAIR units have (2) probes that are inserted through the pipe wall and into the air flow.  Each of the probes has a resistance temperature detector (RTD.) One of the probes measures the temperature of the air flow.  The other probe is heated to maintain a preset temperature difference from the temperature measured by the first probe.  The faster the air flow, the more heat that is required to keep the second probe at the prescribed temperature.  From Heat Transfer principles, the heat energy input required to maintain the preset temperature is based on the mass velocity of the air.  Using basic physical properties for compressed air, the volumetric rate can be determined (SCFM), and displayed.

It is important to note that the compressed air should be filtered to remove oils, and dried to remove water, as these liquids have different physical properties from air, and will cause erroneous readings.

Advantages

  • Easy to install – No cutting or welding required
  • Summing Remote Display and Data Logger available
  • Sensitive at low flows
  • Rugged, reliable and no moving parts
  • No calibration or set-up required
  • Models from 1/2″ to 4″ schedule 40 iron pipe in stock
  • Short lead time for sizes up to 6″ Schedule 40 iron pipe
  • Available for size 3/4″ to 4″ copper pipe
  • New Wireless Capability

If you have any questions about the Digital Flow Meter or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Twitter: @EXAIR_BB

Finding and Fixing Leaks in Your Compressed Air System

I had to find and fix some leaks this week – in my yard. See, my underground storm sewer pipe, that carries my basement sump pump discharge and my house’s gutter drains to the street, was leaking.

The evidence was clear…swampy puddles were developing in my neighbor’s yard.

The location was clear…several patches of grass in MY yard were WAY more green and vibrant than the rest.

The cause was NOT clear…until I dug up those patches of the best looking grass my lawn has ever seen. Turns out, my maple tree’s (the showpiece of my front yard) root system found a way to penetrate one of the couplings in the sewer pipe, where it prospered into this:

That’s about 8ft worth of root growth that was clogging my drain pipe, and causing leaks upstream. My maple tree is not shown in the picture because my maple tree is a real jerk.

Two days worth of digging up and reinstalling pipe later, and all is well.  I mean, except for filling the trench, sowing some new grass seed, watching the birds eat it, sowing some more, etc.  Ah, the joys of home ownership…

I tell you all this, dear reader, so you know that I. Don’t. Like. Leaks…whether they be in my storm sewer pipe or in your compressed air system…which brings me to the (real) subject of my blog today.

Unlike the visual indications of my yard leak, compressed air system leaks don’t really draw much attention to themselves.  Unless they grow quite large, they’re typically invisible and very quiet…much too quiet to be heard in a typical industrial environment, anyway.  Good news is, they’re not all that hard to find.

One way is to use a soap-and-water solution.  You just need a spray bottle, some dish soap, and water.  Spray it on the piping joints, and all but the smallest, most minute, of leaks will create soap bubbles…instant indication of air leakage.  This method is inexpensive and simple, but it does tend to leave little puddles all over.  Plus, if your header runs along the ceiling, you’re going to have to get up there to do it.  And unless you can easily maneuver all the way around the pipe, you can miss a leak on the other side of the joint. If you have a small and relatively simple compressed air system, and all your piping is accessible though, this method is tried and true.

For many industrial compressed air systems, though, the limitations of the soap bubble method make it impractical.  But I’ve got more good news: those silent (to us) air leaks are making a real racket, ultrasonically speaking.  And we’ve got something for that:

EXAIR Model 9061 Ultrasonic Leak Detector discovers and pinpoints leaks, quickly and easily.

See, when a pressurized gas finds its way through the narrow (and usually torturous) path out of a slightly loosened fitting, worn packing on a valve, etc., it creates sound waves.  Some of those ARE in audible frequencies, but they’re often so low as to be drowned out by everything else that’s happening in a typical industrial environment.  Those leaks, however, also create sound waves in ultrasonic frequencies…and EXAIR’s Ultrasonic Leak Detector takes advantage of that ultrasonic racket to show you where those leaks are, as well as give you a qualitative indication of their magnitude.  Here’s how it works:

Find leaks and fix them.  This is Step #2 of our Six Steps To Optimizing Your Compressed Air System.  If you’d like to find out more, give me a call.

Russ Bowman
Application Engineer
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Compressor Control – A Way to Match Supply to Demand

Rarely does the compressed air demand match the supply of the compressor system. To keep the generation costs down and the system efficiency as high as possible Compressor Controls are utilized to maximize the system performance, taking into account system dynamics and storage. I will touch on several methods briefly, and leave the reader to delve deeper into any type of interest.

air compressor

  • Start/Stop – Most basic control –  to turn the compressor motor on and off, in response to a pressure signal (for reciprocating and rotary type compressors)
  • Load/Unload – Keeps the motor turning continuously, but unloads the compressor when a pressure level is achieved.  When the pressure drops to a set level, the compressor reloads (for reciprocating, rotary screw, and centrifugal type)
  • Modulating – Restricts the air coming into the compressor, as a way to reduce the compressor output to a specified minimum, at which point the compressor is unloaded (for lubricant-injected rotary screw and centrifugal)
  • Dual/Auto Dual – Dual Control has the ability to select between Start/Stop and Load /Unload control modes.  Automatic Dual Control adds the feature of an over-run timer, so that the motor is stopped after a certain period of time without a demand.
  • Variable Displacement (Slide Valve, Spiral Valve or Turn Valve) – Allows for gradual reduction of the compressor displacement while keeping the inlet pressure constant (for rotary screw)
  • Variable Displacement (Step Control Valves or Poppet Valves) – Similar effect as above, but instead of a gradual reduction, the change is step like (for lubricant injected rotary types)
  • Variable Speed – Use of a variable frequency AC drive or by switched reluctance DC drive to vary the speed of the motor turning the compressor. The speed at which the motor turns effects the output of the system.

In summary – the primary functions of the Compressor Controls are to match supply to demand, save energy, and protect the compressor (from overheating, over-pressure situations, and excessive amperage draw.) Other functions include safety (protecting the plant and personnel), and provide diagnostic information, related to maintenance and operation warnings.

If you would like to talk about compressed air or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Find us on the Web 
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Twitter: @EXAIR_BB

Lower Operating Costs by Minimizing Compressed Air Leaks

Almost every industry uses compressed air in some capacity. It is often referred to as the “fourth utility” In an industrial setting, next to water, gas and electric. and in many cases, is the largest energy user in the plant. With an average cost of $ 0.25 per every 1000 Standard Cubic Feet used, compressed air can be expensive to produce so it is very important to use this utility as efficiently as possible. When evaluating the performance of a compressed air system, it’s important to look at the system as a whole.

When you operate point-of-use devices at a higher pressure than necessary to perform a certain job or function, you are creating “artificial demand”. This results in excess air volume being consumed, increasing the amount of energy being lost to waste. For example, plant personnel or operators increase the supply pressure in an effort to improve the end use devices performance. When there is a leak in the system, the line pressure will actually begin to drop and performance begins to deteriorate in other areas in the plant. This not only puts stress on the existing compressor but it also leads to the false idea that a larger or secondary compressor is needed.

Here’s a quick reference on how operating pressure can directly affect operating cost:


Our Model # 1101 Super Air Nozzle requires 14 SCFM @ 80 PSIG. Based on the average operating cost of $ 0.25 per 1000 SCF used, it would cost $ 0.21 per hour to operate this nozzle. (14 SCFM x $ 0.25 x 60 minutes / 1000 SCF = $ 0.21)

If you were able to use the same Model # 1101 Super Air Nozzle operating at only 40 PSIG, while still achieving the desired end result, the air demand would decrease to only 8.1 SCFM, reducing the hourly cost to $ 0.12.  (8.1 SCFM x $ 0.25 x 60 minute / 1000 SCF = $ 0.12)

Don’t waste your money

Leaks in a compressed air system can account for up to 30% of the total operational cost of the compressor, wasting thousands of dollars of electricity per year. Some of the more common places for a leak to occur would be at connection points such as valves, unions, couplings, fittings, etc.

In this table, you will see that a certain amount of air volume is lost through an orifice or opening. If you have several leaks throughout your facility, it isn’t gong to take long for the waste and high operating costs to quickly add up as well as potential increases in repair or maintenance costs for the existing compressor. The industry average shows that any leakage more than 10%, shows there are areas where operational improvements could be made in a compressed air system.

Stay tuned to our blog over the next few weeks as we will discuss how following a few simple steps can help optimize your current compressed air system, in many cases, reducing energy costs related to compressed air waste, leading to a more economical operation.

In the meantime, if you have any questions or would like to discuss a particular application or EXAIR product, give me a call at 800-903-9247.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

 

 

A Unique Application for the Ultrasonic Leak Detector

Here on the EXAIR blog we post a ton of different applications for our products. We typically see similar applications each day and write about them so that you may identify potential points in your various processes that may benefit from an engineered compressed air solution. Many of these are typical blowoff or cooling applications that we see day in and day out. Sometimes, though, we see some applications that are outside the realm of typical operation. This can sometimes require the manufacturing of a specialized part or just getting a little creative with a stock product.

Our distributor in Argentina recently contacted me about a unique application for an Ultrasonic Leak Detector. The Model 9061 Ultrasonic Leak Detector is a hand-held instrument that allows you to locate costly leaks in a compressed air distribution system. As pressurized air exits a small orifice, an ultrasonic sound that is above human hearing is created. The Ultrasonic Leak Detector is able to pick up on these sound emissions and can convert it to an audible range that is able to be heard by the human ear. Typically, this product is used in conjunction with a leak prevention program to help save money and compressed air by identifying leaks in the distribution system.

ultrasonic_2
Model 9061 ULD detecting a leak

The customer is a manufacturer of plastic bottles used to hold a wide variety of different personal care products. The bottles were molded in two separate pieces, then brought together and sealed. After the two pieces of the bottle were sealed, they had to test each one to ensure that they remained watertight. Their current method involved filling the cavities with water and inspecting for leaks.

While this method was effective, when a leak was present water would get all over the machine and floor and needed to be cleaned up. This to them was considered a nuisance and they began to explore alternative methods of checking the seals on the bottles. They found EXAIR’s Ultrasonic Leak Detector and wondered if they could use it to detect leaks on the bottles if they were to pressurize them with compressed air instead of filling them with water. We’ve handled similar applications in the past, this one here a customer used the ULD to detect leaks from poor welds on the roof of buses. They ordered one for testing and were very pleased with the results. The ULD had no problem detecting leaks in the bottles and allowed them to eliminate the mess and annoyance associated with using water.

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Operator testing for leaks using the ULD

Just because you can’t find a particular application in our Application Database on the website or here on the blog, doesn’t mean that it can’t be done! With our unconditional 30 day guarantee for all stock products you have plenty of time to test it out in your specific application. If for any reason it won’t work for you, just send it back and we’ll try something else.

If you have a unique application that could be served by an Intelligent Compressed Air Product, give us a call. Trust me when I say we absolutely LOVE tackling a new and exciting challenge with a creative solution!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD