“There are a thousand hacking at the branches of evil to one who is striking at the root.” Henry David Thoreau
This quote is often how I imagine the army of consultants and experts who offer advice on the improvement of - well anything and compressed air is no exception – acts.
Sure a consultant can come in and do some tests and put together a slick report and make recommendations that aren’t practical or even effective because they are hacking at branches.
If you want results from simple actions, you need to tackle the root cause of your problems – like having a dehydration headache and reaching for an aspirin… No! Drink some water and the headache won’t come back after the aspirin wears off…
Here are my top three root causes of issues with your compressed air system problems.
Root Cause #1 – System Design and Implementation.
This covers both the design of the system and the integration of the components of the system to reach the specified performance. You could write an encyclopaedia of all the wrong ways to design a compressed air system.
Once a system has been built and it is not performing as well as desired then a careful plan to adjust the system is required. This has to be a custom plan. There is no one size fits all solution.
Root Cause #2 – Poor Integration.
Often compressed air systems are not so much designed as built like a child’s Lego project. A big catalogue of bits is opened up and those bits are picked and put together to create the system. Then when the system doesn’t perform more bits are added.
Often times the added components are not properly integrated into the original controls so we see things like idle compressors consuming power, etc. Obviously unless there is complete integration the costs for the system to produce a cubic foot of compressed air will be higher than they need to be.
Root Cause #3 – Ineffective Measurement.
In compressed air systems efficiency is measured by output per unit of power E.g. scfm/kW. It’s useful to know this across the loads the system is likely to experience and in various failure modes.
A compressed air system should be designed around optimizing this number. And a system’s performance should be measured and managed against its initial design. Instead we see companies measure the costs to run parts/components of their system.
We often find with a comprehensive measurement in place, that these savings on individual parts don’t translate into savings for the system as a whole.
Obviously, measurement against a design sometimes is impossible because there was no master design for the compressed air system. In that case, I’d work from current situation and start looking for ways to reduce your output per unit of power consumer.
If your compressed air expenses are climbing (or if you can’t measure them accurately) or you think you need to expand your system, the first thing to do is to take stock of the system as a whole. If you don’t have the necessary expertise in-house, we will audit your compressed air system for you and guide you to getting the performance you need. To get started with a no-obligation discussion call 404-363-6000 or drop us a line sales@pyebarker.com
We’re back for another edition of “Know Your Pumps.” This time we take a look at another member of the positive displacement pump family: lobe pumps.
Lobe pumps are similar to external gear pumps in operation, except the pumping elements or lobes do not make contact. Lobe contact is prevented by external timing gears producing a continuous (non-pulsating) discharge.
Pump shaft support bearings are located in the timing gear case. Since the bearings are out of the pumped liquid, pressure is limited by bearing location and shaft deflection. There is not metal-to-metal contact and wear in abrasive applications is minimal. Use of multiple mechanical seals makes seal construction important.
Lobe pumps are frequently used in food applications, because they handle solids without damaging the pump or the product. Lobe pumps can pump much larger particles than can other positive displacement pumps.
Since the lobes do not make contact, and clearances are not as close as in other PD pumps, this design handles low viscosity liquids with diminished performance. Loading characteristics are not as good as other designs, and suction ability is low. High-viscosity liquids require considerably reduced speeds to achieve satisfactory performance.
Lobe pumps are cleaned by circulating a fluid through them. Cleaning is important when the product cannot remain in the pumps for sanitary reasons or when products of different colors or properties are batched.
What Do We Use Them For?
Score Card
| Abrasives
|
Thin
Liquids |
Viscous Liquids | Solids | Dry Prime | Diff. Pressure | |
| How well does a Lobe Pump handle it? |
G |
A |
E |
E |
A |
G |
E = Excellent, G = Good, A = Average, P = Poor
It’s interesting to me that a lot of compressed air systems are allowed to grow organically.
Pumping systems are precisely engineered. Requirements are specified exactly. The system is evaluated on paper, future-proofed. Those designs are evaluated and double checked… Compressed air systems are not specified per se.
Compressed air system components are specified.
A lot of compressed air systems aren’t anywhere near as well engineered. Frankly far too many systems are a built out of a mish-mash of components, often with customization and often there are oversights in integration.
Eli Goldratt wrote a lot of books about using Theory of Constraints in business settings. Initially he was famous for optimizing the production of manufacturing systems. The big mistake he saw in a business was ‘optimizing each step of the process.’ He called it striving for ‘local optima.’
Independently specifying the best compressor, best drying system, best storage tank won’t produce the most overall efficient system.
Ultimately there will be one component that is the constraint on the system and it will determine the overall performance of the system. Kind of like a chain only being as strong as it’s weakest link.
The capacity of your compressed air system will be limited by the ‘weakest link.’
If I was to design a compressed air system from the ground up I would be looking at
Then I’d specify a system based around those criteria.
We know that most systems are already up and running and now many plant managers are having to add capacity or improve air quality or sometimes doing both to their existing compressed air systems. However, when there is no overall system consideration you can end up creating something like Frankenstein’s monster.
For example: if you add a new compressor with a Variable Speed Drive to an existing compressed air system. Say that new compressor runs at 50% speed and power. Say the system’s existing modulating compressor has cut its output and is now running at 20% capacity. That modulating compressor could still be using 75% of its full power load.
The new VSD operated compressor might be able to handle the base load at about 70% capacity and consuming 70% power. Instead, in this example, two compressors are running at 125% of the necessary power.
That’s obviously not optimal.
For a start you’d want is to update the controls for the system so that the VSD compressor handles the base load and the modulating compressor comes on to handle demand over a threshold and it is shut down when demand is below that threshold.
That’s really only the beginning of system optimization.
If your compressed air expenses are climbing (or if you can’t measure them accurately) or you think you need to expand your system, the first thing to do is to take stock of the system as a whole. If you don’t have the necessary expertise in-house, we will audit your compressed air system for you and guide you to getting the performance you need. To get started with a no-obligation discussion call 404-363-6000 or drop us a line sales@pyebarker.com
Sometimes there’s nothing quite like a reminder about the basics of various product categories. So we thought we’d take the time to review some of the major pump categories. Starting with the ever reliable Internal Gear Pump.
The crescent internal gear pump has an outer or rotor gear that is generally used to drive the inner or idler gear. The idler gear, which is smaller than the rotor gear, rotates on a stationary pin and operates inside the rotor gear.
The gears create voids as they come out of mesh and liquid flows into the pump. As the gears come back into mesh, volumes are reduced and liquid is forced out the discharge port. Liquid can enter the expanding cavities through the rotor teeth or recessed areas on the head, alongside the teeth. The crescent is integral with the pump head and prevents liquids from flowing to the suction port from the discharge port.
The rotor gear is driven by a shaft supported by anti friction bearings. The idler gear contains a journal bearing rotating on a stationary pin in the pumped liquid. Depending on shaft sealing arrangements, the rotor shaft support bearings may run in pumped liquid. Abrasive liquid can wear out a support bearing.
The speed of internal gear pumps is considered relatively slow compared to centrifugal types. Speeds of up to 1,150rpm are considered common, although some small designs operate up to 3,450 rpm. Because of their ability to operate at low speeds, internal gear pumps are well suited for high-viscosity applications and where suction conditions call for a pump with minimal inlet pressure requirements.
For each revolution of an internal gear pump, the gears have a fairly long time to come out of mesh allowing the spaces between gear teeth to completely fill and not cavitate. Internal gear pumps have successfully pumped liquids with viscosities above 1,320,000 cSt / 6,000,000 SSU and very low viscosity liquids, such as liquid propane and ammonia.
Internal gear pumps are made to close tolerances and are damaged when pumping large solids. These pumps can handle small suspended particulate in abrasive applications, but gradually wear and lose performance. This can be limited for a time by adjusting the pump end clearance (the closeness of the rotor gear to the head of the pump).
What Do We Use It For?
Score Card
| Abrasives
|
Thin
Liquids |
Viscous Liquids | Solids | Dry Prime | Diff. Pressure | |
| How well does an Internal Gear Pump handle it? |
G |
G |
E |
P |
A |
G |
E = Excellent, G = Good, A = Average, P = Poor
Up until very recently there have been two very good reasons why compressed air systems weren’t monitored beyond temperature and pressure.
Thankfully, technology has come to the rescue and there are now lots of inexpensive instruments that are very accurate. Which means there is no excuse not to measure how your compressed air system performs – it pays to be tracking flow, power energy, dew point and key temperatures over time but this is very rarely done.
Stop and think about it for a second – here is a vital system to your operation. When your compressed air system goes down for planned or unplanned maintenance, the whole plant grinds to a halt or at best you’ve got a fraction of the productivity when it’s running.
On top of this – you are talking about one of your largest single energy cost centers in your plant. Surely you’d like to know if it is running efficiently or you are literally flushing perfectly good money down the toilet, as it runs inefficiently hour after hour, day after day.
All that needs to be done is logging of your data. Which is quite straight forward nowadays too.
“If You Can’t Measure It, You Can’t Improve It.”
Lord Kelvin.
The main purpose of measuring and recording data is so that you can improve performance. If we have a baseline we can see if the system is at least holding steady or if it is becoming less efficient i.e. its specific power is rising.
Having access to logged data over time will give you access to performance trends and valuable feedback when you make changes – did it make your system for efficient?
Identify Maintenance Issues
Just because the compressor controls say ‘everything functioning properly’ doesn’t mean they should be taken as gospel. Having a measuring system in place it means you can verify that what your compressor controls say is true.
Ensuring Pressure Stability
One of the common goals of a compressed air system is to provide a steady supply of compressed air at the right pressure – again, this is hard to monitor without data logging. Compressed air systems can take some wild swings in pressure. Some are just part and parcel of life and some have underlying causes. With data it can be possible to identify reoccurring pressure problems and pinpoint the causes.
Troubleshoot Problems.
When you have a problem, the best thing you can do is go back and review the actual data of what happened rather than rely on the memories of those involved. It’s easier to correct what actually went wrong rather than what you think may have gone wrong.
Verify Your Savings
If senior management is going to spend money improving your equipment they generally want proof that your project is going to pay off. Data logging systems give you that proof. Unfortunately it can mean that if your project fails you’ve got proof of that too. But we know you’re smarter than to recommend a project that won’t improve the operation.
Sizing Equipment
Data on the performance of your compressed air system is a big benefit when working with vendors. Firstly, it means they can’t sell you an over-specked system by exploiting your ignorance. Secondly it means you can have a more informed discussion based on hard data about what you can do to actually reach your goals for your system – be it around energy efficiency, flow rates, or air quality.
It also means you’ll know very fast if your investment was the right one or it wasn’t.
If you’d like to start monitoring the performance of your compressed air system the best thing to do is start with a compressed air audit. As part of the audit Pye-Barker’s team of engineers can design up a robust and inexpensive data monitoring system to suit your compressed air system. To get the process started call 404-363-6000 or drop us a line sales@pyebarker.com
