Receiver Tank Principle and Calculations

 

Visualization of the receiver tank concept

A receiver tank is a form of dry compressed air storage in a compressed air system.  Normally installed after drying and filtration, and before end use devices, receiver tanks help to store compressed air.  The compressed air is created by the supply side, stored by the receiver tank, and released as needed to the demand side of the system.

But how does this work?

The principle behind this concept is rooted in pressure differentials.  Just as we increase pressure when reducing volume of a gas, we can increase volume when reducing pressure.  So, if we have a given volume of compressed air at a certain pressure (P1), we will have a different volume of compressed air when converting this same air to a different pressure (P2).

This is the idea behind a receiver tank.  We store the compressed air at a higher pressure than what is needed by the system, creating a favorable pressure differential to release compressed air when it is needed.  And, in order to properly use a receiver tank, we must be able to properly calculate the required size/volume of the tank.  To do so, we must familiarize ourselves with the receiver tank capacity formula.

An EXAIR 60 gallon receiver tank

Receiver tank capacity formula

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

 

Where,

V = Volume of receiver tank in cubic feet

T = Time interval in minutes during which compressed air demand will occur

C = Air requirement of demand in cubic feet per minute

Cap = Compressor capacity in cubic feet per minute

Pa = Absolute atmospheric pressure, given in PSIA

P1 = Initial tank pressure (Compressor discharge pressure)

P2 = minimum tank pressure (Pressure required at output of tank to operate compressed air devices)

An example:

Let’s consider an application with an intermittent demand spike of 50 SCFM of compressed air at 80 PSIG.  The system is operating from a 10HP compressor which produces 40 SCFM at 110 PSIG, and the compressed air devices need to operate for (5) minutes at this volume.

We can use a receiver tank and the pressure differential between the output of the compressor and the demand of the system to create a reservoir of compressed air.  This stored air will release into the system to maintain pressure while demand is high and rebuild when the excess demand is gone.

In this application, the values are as follows:

V = ?

T = 5 minutes

C = 50 CFM

Cap = 40 SCFM

Pa = 14.5 PSI

P1 = 110 PSIG

P2 = 80 PSIG

Running these numbers out we end up with:

This means we will need a receiver tank with a volume of 24.2 ft.³ (24.2 cubic feet equates to approximately 180 gallons – most receiver tanks have capacities rated in gallons) to store the required volume of compressed air needed in this system.  Doing so will result in a constant supply of 80 PSIG, even at a demand volume which exceeds the ability of the compressor.  By installing a properly sized receiver tank with proper pressure differential, the reliability of the system can be improved.

This improvement in system reliability translates to a more repeatable result from the compressed air driven devices connected to the system.  If you have questions about improving the reliability of your compressed air system, exactly how it can be improved, or what an engineered solution could provide, contact an EXAIR Application Engineer.  We’re here to help.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

What Makes A Compressed Air System “Complete”?

It’s a good question.  When do you know that your compressed air system is complete?  And, really, when do you know, with confidence, that it is ready for use?

A typical compressed air system. Image courtesy of Compressed Air Challenge.

Any compressed air system has the basic components shown above.  A compressed air source, a receiver, dryer, filter, and end points of use.   But, what do all these terms mean?

A compressor or compressed air source, is just as it sounds.  It is the device which supplies air (or another gas) at an increased pressure.  This increase in pressure is accomplished through a reduction in volume, and this conversion is achieved through compressing the air.  So, the compressor, well, compresses (the air).

A control receiver (wet receiver) is the storage vessel or tank placed immediately after the compressor.  This tank is referred to as a “wet” receiver because the air has not yet been dried, thus it is “wet”.  This tank helps to cool the compressed air by having a large surface area, and reduces pulsations in the compressed air flow which occur naturally.

The dryer, like the compressor, is just as the name implies.  This device dries the compressed air, removing liquid from the compressed air system.  Prior to this device the air is full of moisture which can damage downstream components and devices.  After drying, the air is almost ready for use.

To be truly ready for use, the compressed air must also be clean.  Dirt and particulates must be removed from the compressed air so that they do not cause damage to the system and the devices which connect to the system.  This task is accomplished through the filter, after which the system is almost ready for use.

To really be ready for use, the system must have a continuous system pressure and flow.  End-use devices are specified to perform with a required compressed air supply, and when this supply is compromised, performance is as well.  This is where the dry receiver comes into play.  The dry receiver is provides pneumatic capacitance for the system, alleviating pressure changes with varying demand loads.  The dry receiver helps to maintain constant pressure and flow.

In addition to this, the diagram above shows an optional device – a pressure/flow control valve.  A flow control valve will regulate the volume (flow) of compressed air in a system in response to changes in flow (or pressure).  These devices further stabilize the compressed air system, providing increased reliability in the supply of compressed air for end user devices.

Now, at long last, the system is ready for use.  But, what will it do?  What are the points of use?

Points of use in a compressed air system are referred to by their end use.  These are the components around which the entire system is built.  This can be a pneumatic drill, an impact wrench, a blow off nozzle, a pneumatic pump, or any other device which requires compressed air to operate.

If your end use devices are for coating, cleaning, cooling, conveying or static elimination, EXAIR Application Engineers can help with engineered solutions to maximize the efficiency and use of your compressed air.  After placing so much effort into creating a proper system, having engineered solutions is a must.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Spending Some Extra Time Can Save Money (and Stress)

If you are familiar with our blog, you will see where I have recently written about coaching my oldest son’s pee wee football team this year. Things slowed down this past week as the team had a bye so that meant a “free” weekend or as my wife called it – “a chance to do some of the things you have put off over the last few months”. On the top of the list was painting our bedroom.

painting
Not my idea of a fun weekend!

My oldest son loves to help with projects and I never want to discourage him so when he asked if he could help, of course the answer was “yes”. Not only did this mean I had to spend some extra $ to get some supplies “for kids”, as he put it, I also needed to spend some time explaining what he needed to do. As we started to prep the walls, I went ahead and cut in around the ceiling, doors, baseboard and trim. My plan was that I would paint the top portion of the wall while he worked on the lower. I set up his little roller and watched him paint about a 4 foot wide section and much to my surprise he did a pretty good job. My wife needed a hand with our infant son, so I felt somewhat confident leaving our oldest unsupervised for a few minutes. BIG mistake!

When I got back upstairs, he had painted over the baseboard, trim and managed to drip paint all over the hardwood floors. When I asked him what happened, he responded with “well dad, I wanted to hurry because it’s really nice outside and I NEED to go out and play! Besides you said you were going to have to clean up anyway”. Go outside son, PLEASE, go outside and play. Now not only did I have to clean up the paint, but I also had to spend more money on new baseboard and trim because there is no way I was going to be able to salvage his masterpiece. Maybe I should have spent a little while longer explaining the process? Regardless, my next few moments of “free” time have all been filled.

Taking the time to review your compressed air system can be very important to your company’s efficiency. In many industrial settings/facilities, the compressed air system is an opportunity for savings and efficiency. In fact, the largest motor in a plant is often on the compressor itself. Leaving a small compressed air leak unattended or using an inefficient blowoff for a long period of time can result in very expensive electrical waste. This excessive expense and waste can negatively affect a company’s profit margin as well as reduce performance and increase production costs.

Luckily, EXAIR can help optimize your compressed air system by using our 6 Simple Steps:

6 steps

Measure the compressed air usage using a flow meter. Once you have identified your usage, you can work on finding a more efficient alternative.

Use a leak detector to locate expensive, wasteful leaks.

Replace the inefficient sources with a more efficient engineered solution

Operate the compressed air only when it’s needed. Our Electronic Flow Control (EFC) is an ideal choice to use for on/off service or to set up on a timed basis.

Install a Receiver Tank to provide additional compressed air supply for applications requiring large amounts of compressed air.

Control the supply pressure to the device using a regulator. Sometimes operating at lower pressure can still be effective and can reduce the overall energy cost of the operation. 

While I can’t recommend my son to lend (2) little helping hands, I might be able to provide some assistance with optimizing your compressed air system. Give us a call at 800-903-9247 to see how we can help.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

Painting Supplies image courtesy of TedsBlog via Creative Commons License

 

How Much Compressed Air Can YOU Save?

I had the pleasure of speaking with a service technician with a pneumatics company recently…he was finishing up a large project for a customer that involved modifying some machinery to reduce compressed air consumption. After the performance of the newly modified machinery was verified, the customer wanted to know how they could be sure they were indeed saving the amount of air that the project engineer estimated that they would save. That’s when he called to ask about EXAIR Digital Flowmeters.

EXAIR Digital Flowmeters are available for iron pipe up to 6", and copper pipe up to 4".
EXAIR Digital Flowmeters are available for iron pipe up to 6″, and copper pipe up to 4″.

If you follow the famous (to EXAIR blog readers, anyway) Six Steps To Optimizing Your Compressed Air System, you know that this is Step #1. So, was it too late to apply a measurement device? Of course not…in this case, the machinery’s original published compressed air consumption rates were used to compare the new actual usage according to the Digital Flowmeter, and it was simple arithmetic from there.  They installed a Model 9095 Digital Flowmeter for 2″ Iron Pipe on the header supplying the machinery, and were not only impressed with the results of the upgrade, but also enjoy the at-a-glance verification of air flow.

Naturally, if you ask for our assistance in the planning stages of a compressed air optimization project, we’ll encourage you to follow the Six Steps in order. Depending on the nature of the problem(s) and the size & complexity of your system, there may be more or less attention paid to certain steps than others.

For instance, a system that was originally equipped with Receiver Tanks at predetermined locations might allow us to skip right over Step #5. If engineered or automated controls, like our EFC Electronic Flow Control & Pressure Regulators are already incorporated, we can check off Steps #4 and #6.

Receiver Tanks are an ideal solution for intermittent demands for high volumes of compressed air.
Receiver Tanks are an ideal solution for intermittent demands for high volumes of compressed air.
The EFC Electronic Flow Control uses a photoelectric sensor to turn air flow on & off, as needed.
The EFC Electronic Flow Control uses a photoelectric sensor to turn air flow on & off, as needed.
Use an EXAIR Pressure Regulator to limit your air supply pressure to the value necessary to accomplish the task.
Use an EXAIR Pressure Regulator to limit your air supply pressure to the value necessary to accomplish the task.

Regardless of “where” you start with your optimization project, “when” you start should be right now. Leaks and inefficiencies won’t fix themselves. Give us a call, and let’s get started.

Russ Bowman
Application Engineer
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Pneumatic Capacitance

Brian Farno and I attended a compressed air training seminar years ago that highlighted best practices, pitfalls, calculations, efficiency, and a variety of other things facing the compressed air industry.  At the same seminar we also discussed pneumatic capacitance.

As it was laid out, pneumatic capacitance is the stored air within a compressed air system – OK, simple enough.  And, in order for there to be any stored energy, there has to be a pressure differential across the storage device – THIS was an AHA moment for me.

I guess I had never really thought about the need for a pressure differential across the storage device in order for there to really be any air stored.  I’m sure if you go back through the tests and exams I took in college there’s some question about it, and I may have known it somewhere in my studies – but the concept really clicked for me in that seminar and at that moment.

I thought about this when visiting a customer’s facility and hearing them complain of dropping line pressure during compressed air operations.  We went to their compressor room and I saw the compressors and tanks in the photos below.

IMG_1439
(3) 75HP Atlas Copco compressors putting out 300 SCFM each. Two of these provide air to the storage tanks below. The third is for operations unrelated to this blog.
IMG_1440
(3) 2200 gallon receiver tanks

Wow!  All this horsepower and air storage and the line pressure is still dropping?  That seems odd.

So, we checked the input and output pressure of the tanks – less than 2 PSI ΔP, effectively limiting the real ability of the tanks.  At this ΔP the tanks were little more than just an addition to the compressed air plumbing of the facility.

We checked output from the compressor and found they had been deliberately decreased to between 80 and 85 PSI.  So, I recommended to leave the output pressure of the compressors (which feed into the tanks) up to 120 PSIG, and to leave the output pressure of the tanks untouched at 80 PSIG.

This change would allow 3 minutes of steady line pressure for the existing compressed air demand (with compressors still loaded) – per tank!  (Calculations at the bottom of this blog.)

This change, while significant, was only part of the solution for this end user.  The bulk of their solution was the installation of EXAIR Super Air Knives at the point of use, which reduce cooling time, improve throughput, and lower compressed air use.

If you think your application may benefit from an EXAIR solution, contact an EXAIR Application Engineer.

 

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Air calculations:

Receiver tank capacity formula

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

 

Where,

V = Volume of receiver tank in cubic feet

T = Time interval in minutes during which compressed air demand will occur

C = Air requirement of demand in cubic feet per minute

Cap = Compressor capacity in cubic feet per minute

Pa = Absolute atmospheric pressure, given in PSIA

P1 = Initial tank pressure (Compressor discharge pressure)

P2 = minimum tank pressure (Pressure required at output of tank to operate compressed air devices)

 

In this application, the values are as follows:

V = 294 cubic feet (per tank)

T = ?

C = 857 CFM (The application required just under 3,000 cubic feet over a duration of 3.5 minutes.  3000 CF/3.5 min = 857 CFM)

Cap = 600 SCFM

Pa = 14.7 PSI

P1 = 120 PSIG

P2 = 80 PSIG

 

So if we manipulate the volume equation just a bit, considering that we know all the values except T, we come up with the following:

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

Therefore,

T = ( (294(120-80)/((857-600)(14.7)) )  —  (units omitted for sanity)

T = 11760 / 3778

T = 3.11 minutes

Pressure Profile: Where to Measure Your Air Pressure

Generic Layout drawing of compressed air piping system.

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.

  1. At the air compressor discharge. (If using multiple compressors, measure at each.)
  2. If dryers of any type are being used after the compressor measure downstream from the dryer.
  3. 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.)
  4. After each intermediate storage device, such as receiver tanks.
  5. At the point just before the main line from your compressor room branches off to distribution.
  6. The furthest point of each header line you have installed.
  7. 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.

6 steps
The EXAIR Six Steps To Optimizing Your Compressed Air System.

 

If you would like to discuss this or any of the other 6 steps to compressed air optimization, feel free to contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Back To The Basics (of compressed air)…And The Track

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.  20140506_134512That’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.

6 steps

 

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.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF