Ashley Oberkirch

The Rotary Compression Cycle

The compression cycle of a rotary compressor is a continuous process from intake to discharge with no reciprocating mechanisms starting and stopping as found in reciprocating compressors. The compressor consists of two rotors in constant mesh, housed in a cylinder with two parallel adjoining bores. The male drive rotor has four lobes that mesh with six flutes in the female rotor. All parts are machined to exacting tolerances.
As the rotors rotate, (male-clockwise as viewed from the power input end) air is drawn into the cylinder through the inlet port located at the power input end. A volume of air is trapped as the rotor lobes pass the inlet cut off points in the cylinders. Compression occurs as the male rotor rolls into the female flute, progressively reducing the space thereby raising the pressure. Compression continues until the lobe and flute pass the discharge port. The compressed air is then discharged into the air/fluid reservoir. There are four complete compression cycles for each complete rotation of the male rotor.


Compression Cycle

Quincy Compressor Fluids

1Quincy’s fluid analysis program is offered to all customers using QuinSyn fluids in Quincy Compressor Rotary Screw Compressors. This service provides optimum drain intervals for compressors operating on QuinSyn fluids. Monitoring of the total acid number (TAN), barium level and/or viscosity throughout the life of the fluid provides maximum protection to your machine, while best utilizing the extended life features of QuinSyn.

The fluid analysis provides historical information, detailing items such as hours on the fluid, viscosity and total acid number (TAN). Should results appear unusual or suspicious, a detailed analysis can pinpoint specific contaminants. A detailed report is furnished to you, your Quincy Distributor and the Quincy Compressor factory upon completion of the fluid analysis.
Although QuinSyn fluids are rated by hours of life expectancy under normal operating conditions, it is recommended that fluid samples be taken every 500 to 2,000 hours and sent to Quincy Compressor Fluid Analysis until a history of performance in a specific compressor application is established. Once the appropriate drain interval is established, the frequency of the fluid analysis can be reduced unless operating conditions change.

QuinSyn Plus – QuinSyn Plus is the factory fill for Quincy rotary screw compressors. QuinSyn Plus is an ISO 46 viscosity fluid with an 8,000 hour life under normal operating conditions (exact fluid life is determined by the fluid analysis program). It is synthetic hydrocarbon/ester fluid. QuinSyn Plus is suited for use in rotary screw air compressors operating in harsh service conditions where the fluid is exposed to higher temperatures for extended periods of time.

                         Typical Properties of QuinSyn Plus            ISO 46
        Viscosity @ 100ºF ASTM D445 46.0 cSt.
        Viscosity @ 210ºF ASTM D445 7.5 cSt.
      Viscosity Index ASTM D2270 127
   Specific Gravity 60/60 0.89
   Flash Point ASTM D92 475ºF
  Fire Point ASTM D92 540ºF
Pour Point -58ºF


QuinSyn PG – QuinSyn PG is a custom blended polyalklene glycol/ester (PAG). QuinSyn PG is an ISO 46 viscosity fluid with an 8,000 hour life under normal operating conditions. QuinSyn PG is the recommended fluid in high humidity applications due to its ability to hold water. QuinSyn PG is best suited for applications where high humidity exists and the machine cannot be shut down to drain water from the reservoir.

                       Typical Properties of QuinSyn PG                      ISO 46
Viscosity @ 100ºF ASTM D445 52.4 cSt.
Viscosity @ 210ºF ASTM D445 9.4 cSt.
Viscosity Index ASTM D2270 163
Specific Gravity 60/60 0.98
Flash Point ASTM D92 485ºF
Fire Point ASTM D92 525ºF


QuinSyn XP – QuinSyn XP is the factory fill for high pressure units (defined as units over 150 psig full flow). QuinSyn XP is a custom blended polyolester (POE) fluid ideally suited for rotary screw air compressors. QuinSyn XP is an ISO 68 viscosity fluid with a 12,000 hour life at 100 & 125 psig full flow under normal operating conditions and 8,000 hours as a high pressure fluid. QuinSyn XP is designed for application where the fluid is exposed to elevated temperatures for extended periods of time.

                    Typical Properties of QuinSyn XP                        ISO 68
Viscosity @ 100ºF ASTM D445 43.0 cSt.
Viscosity @ 210ºF ASTM D445 7.5 cSt.
Viscosity Index ASTM D2270 139
Specific Gravity 60/60 0.83
Flash Point ASTM D92 495ºF
Fire Point ASTM D92 560ºF
Pour Point -76ºF

QuinSyn F – QuinSyn F is Quincy’s food grade fluid suitable in applications where there may be incidental food contact. Compliant with FDA 21 CFR 178.3570 (Lubricants with Incidental Food Contact), QuinSyn F is authorized by the USDA with an H-1 rating for use in federally inspected meat and poultry plants. Since the fluid is viewed as a possible indirect food additive, the limit for food contact is 10 ppm. Near white in color and low in volatility, QuinSyn F is ideal for clean service.


                      Typical Properties of QuinSyn F                        ISO 68
Viscosity @ 100ºF ASTM D445 43.0 cSt.
Viscosity @ 210ºF ASTM D445 7.5 cSt.
Viscosity Index ASTM D2270 139
Specific Gravity 60/60 0.83
Flash Point ASTM D92 495ºF
Fire Point ASTM D92 560ºF
Pour Point -76ºF

QuinSyn Flush – QuinSyn Flush is specifically formulated synthetic fluid capable of dissolving varnish and solubilizing sludge from lubricating systems while they are operating. QuinSyn Flush contains oxidation and rust inhibitors, and can be used as a short-term fluid (maximum of 500 hours). It is fully compatible with mineral oils and QuinSyn synthetic fluids, and is highly recommended for use as a flushing fluid when converting to QuinSyn PG from QuinSyn Plus or QuinSyn XP.

                   Typical Properties of QuinSyn Flush                   ISO 68
Viscosity @ 100ºF ASTM D445 43.3 cSt.
Viscosity @ 210ºF ASTM D445 5.6 cSt.
Viscosity Index 65
Specific Gravity 60/60 0.965
Flash Point ASTM D92 444ºF
Fire Point ASTM D92 520ºF
Pour Point -45ºF

What is the difference between a single stage and two stage compressor?

Reciprocating compressors are often some of the most critical and expensive systems at a production facility, and deserve special attention. A frequently asked question regarding reciprocating compressors is how can you tell the difference between a single stage and two stage compressor. The two stages are detailed below: 

Single Stage Compressors

During the downstroke of a single stage compressor, air is drawn through an intake valve in the head of the compressor and into the cylinder. At the bottom of the stroke, the intake valve closes and the air is trapped in the cylinder. The air is then compressed in the cylinder during the upstroke of the piston. Total compression, from atmospheric pressure to the finalQP-15-PressureLubedPump-NoFilters discharge pressure, is accomplished in one stroke of the piston.


Two Stage Compressors

During the downstroke of the piston of a two stage compressor, air is drawn through an intake valve in the head of the compressor into the low pressure cylinder and compressed during the upstroke of the piston.

The compressed air is then released through a discharge valve in the head of the compressor to an intercooler (usually finned tubing) where the heat resulting from compression is allowed to dissipate. The cooler compressed air is then drawn into a second compression cylinder, the high pressure cylinder, for compression to final pressure.

From there the compressed air is released through a discharge valve to an air receiver tank or directly to a network of compressed air supply lines. In one revolution of the crankshaft a compression cycle is completed.

Keeping Customers When Things Go Wrong

Keeping customers makes good business sense but it’s not always easy. One easy question to ask is “Do you know if your customers are happy”? If not, then you should. It’s imperative that you understand what makes your customer happy. Otherwise, you might lose them to a competitor. Unfortunately, more customers are willing to discuss how unhappy they are with you or the poor experience they had with your customer service compared to their love for your company. We all know that customers are our biggest assets. Don’t give them a reason to leave and if they are unhappy, Jeff Mowat perfectly discusses “Five Keys to Turning Upset Customers into Fans”. Give us your thoughts/feedback on this important topic in the comments section below. 

Five keys to turning upset customers into fans
by Jeff Mowat

When it coupset customersmes to dealing with dissatisfied customers, most business owners and managers believe that money back guarantees and/or exchange policies will fix the problem.  Lousy strategy.  Money back guarantees and exchanges may fix the problem, but they do nothing to fix the relationship.  Policies don’t fix relationships — people do.

When I speak at conventions and meetings on how to boost customer retention, I often find that there is little attention paid to how employees can fix the damaged relationship when the customer has been let down.  The consequences of this are staggering.

Inadequately trained front line employees chase away repeat customers and referrals, spread damaging word-of-mouth advertising, and become frustrated and de-motivated because they’re constantly dealing with upset customers.

On the other hand, by applying just a few critical people skills, front line employees can create such positive feelings — for both themselves and their customers, that an upset customer will become even more loyal.  They’ll be transformed from being a critic of your organization to becoming an advocate.  Here are 5 key strategies:

1.   Focus on concerns versus complaints.

No one likes to hear customers complain.  Employees become impatient and defensive when faced with these “trouble-makers.”  One of my seminar participants equated listening to customer complaints to undergoing amateur eyeball surgery.  (That can’t be good).

To prevent this defensive mindset, employees need to be trained to treat customer complaints as concerns.  Employees should be made aware of the fact that customers who express concerns are helping you to stay sharp, competitive and successful.  Focusing on a customer concerns vs complaints will immediately shift a potentially negative situation into one that is positive, helpful, and productive.

2.  Empower front-line employees.

For their 43rd wedding anniversary, my father called a florist to order 43 roses for my mother.  When Dad asked for the price, the clerk quoted the single rose price times 43.  She offered no quantity discount despite the fact that they’re usually cheaper by the dozen.  She admitted that this didn’t make sense, adding that her boss wasn’t in and the policy was to issue no discounts without the manager’s approval.  Result — a competitor got the order and Dad will never go back to the first florist.

The lesson is that you can often prevent customers from becoming upset if you empower your front line employees to make reasonable on-the-spot decisions.  This type of delegation require two important factors: training and trust.  The irony is that a lot of managers say they can’t afford to train employees, when in fact they can’t afford not to.  You don’t get customers for free.  You earn customers by investing in front line training.

3.  Prove that you’re listening.

When a customer is voicing their dissatisfaction, stop whatever you’re doing, turn towards them and give them an expression of total concern.  Listen without interrupting.

Then prove that you’ve heard them.  That means repeating and paraphrasing.  Important: make sure you tell them why you’re repeating what they’ve said.  For example, you might say, “I want to make sure I’ve got this straight . . . ”  (then you paraphrase and repeat).  That ensures that the customer knows that you truly understand the problem.

4.  Express sincere empathy.

Virtually every upset customer feels frustrated because they didn’t get what they expected.  It’s that simple.  Whether or not they have a valid reason for feeling frustrated is completely irrelevant.  Upset customers need to know that you care — not just about their problem — but about their frustration.  So, empathize.  That’s something that no refund or exchange will ever do.  Use phrases like, “Gosh, that sounds frustrating.”  Or, “I’d feel the same way if I were you.”  Empathizing will diffuse an angry customer faster than any thing else you can do.

5.  Apologize and provide extras.

Tell the customer, “I’m sorry.”  Even if it wasn’t your fault, but your co-worker’s, you represent your organization to that customer, so apologize on behalf of the entire company.  Even when you suspect the customer may have erred, it’s better to give the customer the benefit of the doubt, than to be “right”  and loose a lifetime of repeat and spin-off business.

If your product or service really did fall short of the mark, then to retain the customer, of course you’d give them a refund or exchange.  But that’s not enough.  On top of the exchange or refund, give them something for their inconvenience.  Any small gesture or token of appreciation (that doesn’t force them to spend more money) will be greatly appreciated and will transform that upset customer into one of your greatest advocates.

The Training Solution

Every business has occasions where things go wrong and customers are disappointed.  When that happens, your customer base won’t be preserved by money back guarantees or exchanges.  Rather, your business will be saved by properly trained front line employees.

Is A Variable Speed Drive (VSD) Compressor the Right Choice for your Facility?

The simple economic model of matching supply with demand optimizes productivity and helps control costs. This makes sense not only in the economic world, but also when considering how compressed air is produced and used in a manufacturing facility.

CompreCAGI bookssed air is critical to a wide range of functions within manufacturing. But poorly designed and maintained compressed air systems, by some estimates, account for significant energy losses and waste every year. One quick and easy way to ensure your facility is not squandering energy in its compressed air production process is to consider the benefits that can be provided by a properly sized variable speed drive compressor.

While many plants require continuous, round-the-clock operations seven days a week, there likely are times when lulls in production present opportunities for energy savings. For example, there are 168 hours in a week and many compressed air systems only require full capacity between 60 and 100 hours, or about half the time. When this partial demand load even occurs, the air compressor output capacity must be regulated or stopped. With units 15 HP or larger, it is not feasible to stop and start the air compressor motor several times an hour throughout the day, so a form of inlet control regulation is the choice. Whether you run the unit with a Load/No-load control (fully loaded or closed inlet for unload and bleed-down) or Modulation (cutting back the inlet throttle plate) to accomplish a partial load run-time, these control systems may not be the most efficient.

Operating a car is a very good example; when you exit the highway, you go from highway speed (let’s say optimum full load at 55 MPH) and then you come to a stop at the bottom of the ramp. There, the car is idling and wasting energy as long as it sits at the stop sign.  City driving is even worse or similar to a very fluctuating demand – starting and stopping, but idling at every stoplight. Now, think of your car sitting (idling) at stop signs and lights for 60 to 100 hours per week.

A compressed air energy audit or assessment including a review of the demand profile, compressed air usage patterns, available air storage capacity and piping network, and the operating environment, all play an integral role in determining if a VSD compressor can provide the energy efficiency you desire.


Variable Speed Drive Technology Supplies Power When Needed

Properly sized Variable Speed Drive compressors, offer the capability to fine-tune a compressor output precisely to fluctuating compressed air demands. By varying the speed of its drive motor, as demand decreases, the VSD lowers the delivered air flow as well as the electrical power consumption in a largely linear fashion. This reduces energy consumption to a minimum when fluctuating demand is the norm. In fact; due to the comparatively low in-rush currents inherent in variable speed drive motor designs, some VSD compressors will stop at the lower compressed air demands vs. idling at unloaded conditions. Even with several starts per hour there is not an issue, so wasteful energy (idling time) is virtually eliminated.


The Business Case

Statistics compiled through compressed air system assessments and performance analysis show that many air compressor applications are ideal for VSD. Compared to a fixed speed drive compressor, a VSD compressor, properly sized for the same end use, can yield significant power savings. In some cases, based on the demand profile, compressed air costs have been reduced by one-third. Another thing to remember is that, due to economic cycles and shifting of manufacturing to other countries, many facilities have significantly reduced the volume of compressed air needed and are therefore operating oversized air compressors. This highlights the need to review the facility compressed air needs when significant production and compressed air demand profiles change. In addition, many local municipalities and state utilities offer rebate incentives for energy savings compressed air solutions, of which VSD technology qualifies.

Energy costs, already on the rise in recent years, have garnered additional attention of late as facility managers are continually charged with finding new ways to cut costs. Many corporations have instituted
“green” policies with aggressive annual energy reduction targets.

Let’s consider a situation where a manufacturer’s compressor system was running a single 200 horsepower air compressor. The operation has fluctuating compressed air demands 24 hours a day at 3 cents per kWh. These energy costs have doubled in the last five years, increasing in some areas to 8 cents per kWh or more. The annual cost to operate that compressor at 3 cents per kWh was $41,273. Today, at 8 cents per kWh, that same compressor costs $110,062 to operate every year, or more than a half a million dollars over five years. After a detailed compressed air demand assessment, it is determined that the fluctuations were within the control range and averaged 35% less than the full capacity of the compressor and the factory had inadequate storage. In this case, switching to a properly sized VSD compressor could potentially save this facility $38,521 annually or more than $192,000 in five years, if the current conditions remain similar over that time period.

Combine these savings with the greater efficiency that is realized when you replace older equipment with newer, more efficient machines and the return on investment with many of these installations is often realized in less than two years. Not every installation can yield this kind of payback, that is the purpose of a professional air demand assessment and proper compressor selection, but for sure…it is worth the consideration.

In summary, by varying output to meet compressed air demands, manufacturers who choose a properly sized VSD compressor as part of their infrastructure can realize immediate energy savings that will only compound over time.


So technically, how does it work?

The VSD concept simply measures the system pressure and maintains a constant delivery pressure within a narrow pressure band. This is achieved by regulating the motor speed of the compressor by frequency conversion, which results in varying air flow delivery. With today’s advanced VSD electronic controls the delivery pressure is kept within a + 1.5 psi band – this is another benefit of systems with a VSD compressor; systems with all fixed speed compressors typically have a minimum 10-15 psig pressure fluctuation. Therefore, a lower air compressor delivery pressure can be used to maintain the required minimum working pressure of the system – which results in increased energy savings and profitability. Remember, for every 2 psi reduction in pressure, power consumption is reduced by 1 percent. That’s more than a 6 percent energy savings just due to the lower operating pressure often made possible by having at least one VSD compressor.

The inverter in the VSD system performs a “soft” start operation by ramping up the motor speed, thus eliminating amperage draw peaks that are typical when a fixed speed motor is started. Power companies usually will impose penalties for these amperage peaks in the form of higher rates. The soft starting utilized by a VSD compressor also helps protect electrical and mechanical components from the starting mechanical stresses that can shorten the life of an air compressor.

For more detailed information about VSD technology applications or answers to any of your compressed air questions, please contact the Compressed air and Gas Institute. The Compressed air and Gas Institute is the united voices of the compressed air industry, servings as the unbiased authority on technical, educational, promotional and other matters that affect compressed air and gas equipment suppliers and their customers. CAGI educational resources include e-learning coursework on the SmartSite, selection guides, videos with the Compressed Air & Gas Handbook. For more information, visit the CAGI web site at This article published by CAGI Promotional Subcommittee on their website,

What Causes Pressure Drop?

Pressure drop is a term used to characterize the reduction in air pressure from the compressor discharge to the actual point-of-use. Pressure drop occurs as the compressed air travels through the treatment and distribution system. A properly designed system should have a pressure loss of much less than 10 percent of the compressor’s discharge pressure, measured from the receiver tank output to the point-of-use.

Excessive pressure drop will result in poor system performance and excessive energy consumption. Flow restrictions of any type in a system require higher operating pressures than are needed, resulting in higher energy consumption. Minimizing differentials in all parts of the system is an important part of efficient operation. Pressure drop upstream of the compressor signal requires higher compression pressures to achieve the control settings on the compressor.
The most typical problem areas include the aftercooler, lubricant separators, and check valves. A rule of thumb for systems in the 100 psig range is: for every 2 psi increase in discharge pressure, energy consumption will increase by approximately 1 percent at full output flow (check performance curves for centrifugal and two-stage, lubricant-injected, rotary screw compressors). There is also another penalty for higher-than-needed pressure. Raising the compressor discharge pressure increases the demand of every unregulated usage, including leaks, open blowing, etc. Although it varies by plant, unregulated usage is commonly as high as 30 to 50 percent of air demand.

For systems in the 100 psig range with 30 to 50 percent unregulated usage, a 2 psi increase in header pressure will increase energy consumption by about another 0.6 to 1.0 percent because of the additional unregulated air being consumed. The combined effect results in a total increase in energy consumption of about 1.6 to 2 percent for every 2 psi increase in discharge pressure for a system in the 100 psig range with 30 to 50 percent unregulated usage. An air compressor capacity control pressure signal is normally located at the discharge of the compressor package. When the signal location is moved downstream of the compressed air dryers and filters to achieve a common signal for all compressors, some dangers must be recognized and precautionary measures taken. The control range pressure setting must be reduced to allow for actual and potentially increasing pressure drop across the dryers and filters.

Provision also must be made to prevent exceeding the maximum allowable discharge pressure and drive motor amps of each compressor in the system. Pressure drop in the distribution system and in hoses and flexible connections at points-of-use results in lower operating pressure at the points-of-use. If the point-of use operating pressure has to be increased, try reducing the pressure drops in the system before adding capacity or increasing the system pressure. Increasing the compressor discharge pressure or adding compressor capacity results in significant increases in energy consumption. Elevating system pressure increases unregulated uses, such as leaks, open blowing, and production applications, without regulators or with wide open regulators.

The added demand at elevated pressure is termed “artificial demand,” and substantially increases energy consumption. Instead of increasing the compressor discharge pressure or adding additional compressor capacity, alternative solutions should be sought, such as reduced pressure drop and strategic compressed air storage. Equipment should be specified and operated at the lowest efficient operating pressure.

What Causes Pressure Drop?
Any type of obstruction, restriction, or roughness in the system will cause resistance to air flow and cause pressure drop. In the distribution system, the highest pressure drops usually are found at the pointsof- use, including undersized or leaking hoses, tubes, disconnects, filters, regulators and lubricators (FRLs). On the supply side of the system, air/lubricant separators, aftercoolers, moisture separators, dryers and filters can be the main items causing significant pressure drops. The maximum pressure drop from the supply side to the points-of-use will occur when the compressed air flow rate and temperature are highest. System components should be selected based upon these conditions and the manufacturer of each component should be requested to supply pressure drop information under these conditions. When selecting filters, remember that they will get dirty.

Dirt loading characteristics are also important selection criteria. Large end users who purchase substantial quantities of components should work with their suppliers to ensure that products meet the desired specifications for differential pressure and other characteristics. The distribution piping system often is diagnosed as having excess pressure drop because a point-of-use pressure regulator cannot sustain the required downstream pressure. If such a regulator is set at 85 psig and the regulator and/or the upstream filter has a pressure drop of 20 psi, the system upstream of the filter and regulator would have to maintain at least 105 psig. The 20 psi pressure drop may be blamed on the system piping rather than on the components at fault. The correct diagnosis requires pressure measurements at different points in the system to identify the component(s) causing the excess pressure drop. In this case, the filter element should be replaced of the filter regulator size needs to be increased, not the piping.

Minimizing Pressure Drop
Minimizing pressure drop requires a systems approach in design and maintenance of the system. Air treatment components, such as aftercoolers, moisture separators, dryers, and filters, should be selected with the lowest possible pressure drop at specified maximum operating conditions. When installed, the recommended maintenance procedures should be followed and documented.

Additional ways to minimize pressure drop are as follows:
• Properly design the distribution system.
• Operate and maintain air filtering and drying equipment to reduce the effects of moisture, such as pipe corrosion.
• Select aftercoolers, separators, dryers and filters having the lowest possible pressure drop for the rated conditions.
• Reduce the distance the air travels through the distribution system.
• Specify pressure regulators, lubricators, hoses, and connections having the best performance characteristics at the lowest pressure differential. These components must be sized based upon the actual rate of flow and not the average rate of flow.