How to Size a Receiver Tank and Improve your Compressed Air System

Receiver Tank: Model 9500-60

My colleague, Lee Evans, wrote a blog about calculating the size of primary receiver tanks within a compressed air system.  (You can read it here: Receiver Tank Principle and Calculations).  I would like to expand a bit more about secondary receiver tanks.  They can be strategically placed throughout the plant to improve your compressed air system.  The primary receiver tanks help to protect the supply side when demands are high, and the secondary receiver tanks help systems on the demand side to optimize performance.

Circuit Board

I like to compare the pneumatic system to an electrical system.  The receiver tanks are like capacitors.  They store energy produced by an air compressor like a capacitor stores energy from an electrical source.  If you have ever seen an electrical circuit board, you notice many capacitors with different sizes throughout the circuit board (reference photo above).  The reason is to have a ready source of energy to increase efficiency and speed for the ebbs and flows of electrical signals.  The same can be said for the secondary receiver tanks in a pneumatic system.

To tie this to a compressed air system, if you have an area that requires a high volume of compressed air intermittently, a secondary receiver tank would benefit this system.  There are valves, cylinders, actuators, and pneumatic controls which turn on and off.  And in most situations, very quickly.  To maximize speed and efficiency, it is important to have a ready source of air nearby to supply the necessary amount quickly.

For calculating a minimum volume size for your secondary receiver tank, we can use Equation 1 below.  It is the same as sizing a primary receiver tank, but the scalars are slightly different.  The secondary receivers are located to run a certain machine or area.  The supply line to this tank will typically come from a header pipe that supplies the entire facility.  Generally, it is smaller in diameter; so, we have to look at the air supply that it can feed into the tank.  For example, a 1” NPT Schedule 40 Pipe at 100 PSIG can supply a maximum of 150 SCFM of air flow.  This value is used for Cap below.  C is the largest air demand for the machine or targeted area that will be using the tank.  If the C value is less than the Cap value, then a secondary tank is not needed.  If the Cap is below the C value, then we can calculate the smallest volume that would be needed.  The other value is the minimum tank pressure.  In most cases, a regulator is used to set the air pressure for the machine or area.  If the specification is 80 PSIG, then you would use this value as P2.  P1 is the header pressure that will be coming into the secondary tank.  With this collection of information, you can use Equation 1 to calculate the minimum tank volume.  So, any larger volume would fit the requirement as a secondary receiver tank.

Secondary Receiver tank capacity formula (Equation 1)

V = T * (C – Cap) * (Pa) / (P1-P2)

Where:

V – Volume of receiver tank (cubic feet)

T – Time interval (minutes)

C – Air demand for system (cubic feet per minute)

Cap – Supply value of inlet pipe (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Header Pressure (PSIG)

P2 – Regulated Pressure (PSIG)

If you find that your pneumatic devices are lacking in performance because the air pressure seems to drop during operation, you may need to add a secondary receiver to that system.  For any intermittent design, the tank can store that energy like a capacitor to optimize the performance.  EXAIR stocks 60 Gallon tanks, model 9500-60 to add to those specific locations, If you have any questions about using a receiver tank in your application, primary or secondary, you can contact an EXAIR Application Engineer.  We can restore that efficiency and speed back into your application.

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

 

Photo: Circuit Board courtesy from T_Tide under Pixabay License

Video Blog: EXAIR’s Efficiency Lab

If you’d like to know how efficient (or not,) quiet (or not,) and effective (or not) your current compressed air devices are, the EXAIR Efficiency Lab can help.  For more details, we hope you’ll enjoy this short video.

If you’d like to talk about getting the most out of your compressed air system, we’d love to hear from you.

Russ Bowman
Application Engineer
EXAIR Corporation
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Wet Receivers and Condensate Drains

Receiver Tank

For properly designed compressed air systems, air compressors will use primary storage tanks, or receivers.  They are necessary to accommodate for fluctuations in airflow demand and to help prevent rapid cycling of the air compressor.  (Reference: Advanced Management of Compressed Air – Storage and Capacitance)  There are two types of primary receivers, a wet receiver tank and a dry receiver tank.  The wet receiver is located between the air compressor and the compressed air dryer where humid air and water will be stored.  The dry receiver is located after the compressed air dryer.  In this blog, I will be reviewing the wet receivers and their requirements as a storage tank.

Air compressors discharge hot humid air created by the internal compression.  A byproduct of this compression is water.  By placing a wet receiver on the discharge side of the air compressor, this will create a low velocity area to allow the excess water to fall out.  It will also give the hot air time to cool, allowing the compressed air dryers to be more effective.  With wet receivers, it will reduce cycle rates of your air compressors for less wear and store compressed air to accommodate for flow fluctuations in your pneumatic system.

But, there are some disadvantages with a wet receiver.  For compressed air dryers, it is possible to exceed the specified flow ratings.   If the demand side draws a large volume of air from the supply side, the efficiency of the compressed air dryers will be sacrificed, allowing moisture to go downstream.  Another issue with the wet receiver is the amount of water that the air compressor is pumping into it. As an example, a 60 HP air compressor can produce as much as 17 gallons of water per day.  As you can see, it would not take long to fill a wet receiver.  So, a condensate drain is required to get rid of the excess water.

Condensate drains come in different types and styles.  They are connected to a port at the bottom of the wet receiver where the water will collect.  I will cover the most common condensate drains and explain the pros and cons of each one.

  • Manual Drain – A ball valve or twist drain are the least efficient and the least expensive of all the condensate drains. The idea of having personnel draining the receiver tanks periodically is not the most reliable.  In some cases, people will “crack” the valve open to continuously drain the tank.  This is very inefficient and costly as compressed air is being wasted.
  • Timer Drain Valves – These valves have an electric timer on a solenoid to open and close a two-way valve or a ball valve. The issue comes in trying to set the correct time for the open and close intervals.  During seasonal changes, the amount of water going into the wet receiver will change.  If the timer is not set frequent enough, water can build up inside the receiver.  If too frequent, then compressed air is wasted.  Compared to the manual valve, they are more reliable and efficient; but there is still potential for compressed air waste.

    Timer Relay
  • No-waste Drains – Just like the name, these drains are the most efficient. They are designed with a float inside to open and close a drain vent.  What is unique about the float mechanism is that the drain vent is always under water.  So, when the no-waste drain is operating, no compressed air is being lost or wasted; only water is being drained.  The most common problem comes with rust, sludge, and debris that can plug the drain vent.

All wet receivers require a condensate drain to remove liquid water.  But, the importance for removing water without wasting compressed air is significant for saving money and compressed air.  EXAIR also has a line of Intelligent Compressed Air® products that can reduce your compressed air waste and save you money.  You can contact an Application Engineer for more details.

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

 

Photo: Timer Relay by connectors distribution box.  Attribution – CC BY-SA 2.0