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

When to Use a Receiver Tank for a Compressed Air Application

Recently, I worked with a production engineer at a Tier 1 supplier for the auto industry.  An upcoming project was in the works to install a new line to produce headlight lenses.  As a part of the process, there was to be a “De-static / Blow-off” station, where a shuttle system would bring a pair of the parts to a station where they would be blown off and any static removed prior to being transferred to a painting fixture and sent off for painting.  For best results, the lenses were to be dust and lint free and have no static charge, ensuring a perfect paint result.

The customer installed a pair of 18″ Gen4 Super Ion Air Knives, to provide coverage of the widest 16″ lens assembly, that were staged in pairs.

112212
The Super Ion Air Knife Kit, and Everything that is Included.

The customer was limited in compressed air supply volume in the area of the plant where this process was to occur. 50 SCFM of 80 PSIG was the expected air availability at peak use times, which posed a problem –  the Super Ion Air Knives would need up to 105 SCFM if operated at 80 PSIG.  A further review of the design parameters for the process revealed that the system needed to blow air for only 4 seconds and would be off for 25 seconds to meet the target throughput.

This scenario lends itself perfectly to the use of a Receiver Tank.  Running all of the design numbers into the calculations, showed that the 60 Gallon Receiver Tank we offer, would allow for a 20 second run-time, and require 13.1 seconds to refill.  These figures were well within the requires times, and would allow for the system to work as needed, without having to do anything to the compressed air supply system.

receiver_tank
60 Gallon Receiver Tank

The moral of the story is – if you have a process that is intermittent, and the times for and between blow-off, drying, or cooling allows, a Receiver Tank can be used to allow you to get the most of your available compressed air system.

Note – Lee Evans wrote an easy to follow blog that details the principle and calculations of Receiver Tanks, and it is worth your time to read here.

If you would like to talk about 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

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

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
Find us on the Web
Follow me on Twitter
Like us on Facebook

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