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Paper Number: 033014An ASAE Meeting Presentation

Milking System Air Consumption When Using a Variable Speed Vacuum Pump

Scott A. Sanford, Sr. Outreach Specialist sasanford@wisc.edu

University of Wisconsin

Biological Systems Engineering

460 Henry Mall, Madison, WI 53706

Written for presentation at the 2003 ASAE Annual International Meeting

Sponsored by ASAE Riviera Hotel and Convention Center

Las Vegas, Nevada, USA 27- 30 July 2003

Abstract. Variable speed (VS) vacuum pumps have been on the commercial market for about 8 years yet no one has published a method for providing an accurate estimate of the amount of savings expected from the conversion of a constant speed vacuum pump to a variable speed pump other than using a flat percentage (50% is the most common percentage used). Four farms with existing VS vacuum pumps were monitored for one milking each in an attempt to identify a value of air consumption per milking unit that might be used for estimating air consumption. The range was found to be from 28 LPM to 78 LPM and was not related to parlor size, turns per hour or cows milked per hour. Other factors explored were the influence of milking unit attachment method, long milk hose ID size and milking unit inlet nipple ID size. System leakage or air consumption by vacuum detachers may also be a factor in the wide variation of air consumption per milking unit. All farms had vacuum pumps that were from 39% to 98% larger than the ASAE 518 Standard suggests be used to meet the vacuum system performance requirements. An air consumption rate of 55 LPM was found to give a reasonable estimate for three of the four farms.

Keywords. Variable Speed drive, Vacuum pump, Energy conservation, Energy consumption, Milking machines

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Introduction Variable speed drives were first used in the 1930’s and consisted of a constant speed AC motor driving a DC generator. The generator’s DC output was varied using a rheostat and was used to drive a DC motor. This system was used until the late 1960’s when the Electric Regulator Company developed a solid state relay controller to convert AC power directly to rectified DC power using thyristors. This technology was adapted by all manufacturers of variable speed drives. AC vector technology was developed during the 1980’s but was generally restricted to 75 and larger HP motors until a pulse width modulated sine coded inverter was developed in the late 1980’s. Today with faster, lower priced computer chips and increased sales, inverter costs have declined dramatically.

In the late 1980’s as an outgrowth of the Energy Integrated Dairy System project at Cornell University, Ludington, Aneshansley, Pellerin & Guo began researching ways to reduce vacuum pump energy requirements, which is one of the major energy costs of milk harvesting. This research led to a system using an adjustable speed drive, 3 phase motor, pressure transducer and microprocessor driving a rotary vane vacuum pump (1990). The first commercially available units appeared on the market in the mid 1990’s using blower pumps instead of rotary vane pumps because of issues of vane chatter at low speeds on rotary vane pumps. Despite being on the market for about 8 years, an accurate method of determining the potential energy savings a farmer might realize from a variable speed vacuum pump has not been published. Most companies are estimating a minimum of 50% savings. However, in most cases the savings is substantially greater than 50% and in a few cases the savings is less. A summary of a Cornell University study indicated the average savings to be 70% with a range from 53% to 82%, and the results of a field study by the Bonneville Power Administration showed an average of 68% energy savings with a range from 43% to 78%.

This paper will describe a method for measuring the air consumption when using a variable speed drive and show the results of measurements on four dairy farms. This method can also be used to determine air consumption of different milking units. Four different types of milking units were selected and air consumption was measured for a simulated unit fall-off and the air consumption of one teat cup. Other factors that effect air consumption will also be discussed.

Data Acquisition Equipment: 1) Analog Devices A/D board with a 5B32 Isolated Current input module

a. Input 4mA – 20 mA, Output 0-5 VDC 2) Compaq Laptop computer w/ LabView software (National Instruments) 3) BK Test Bench multi meter - model 388A * 4) Fluke Y8101 AC Current Transformer, 2-150 Amp range, Output 0-150 mA AC * 5) Surge Air Flowmeter w/ adapter (No. 88935), Range 0 to 300 CFM 6) BouMatic Digital Vacuum gauge – P/N 8501503 7) Dent Elite Pro Power data logger with 100 or 150 amp current transformers

Procedure:Two of the milking equipment manufacturers are using an ABB ASC-600 variable frequency drive which has a programmable analog output. These units can be programmed to output a signal directly proportional to the motor speed (RPM), which can be correlated to vacuum pump air flow by generating a calibration curve. The data acquisition was done as follows:

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An Analog Devices A/D board with a 5B32 Isolated Current input module was used to record a 4mA to 20mA signal output from an ABB Variable Frequency Drive model ASC 600 (VFD) which was programmed to be proportional to the motor speed (RPM). A sampling rate of 12 hertz was used. A calibration test run was preformed to relate the motor speed in RPM to the vacuum pump capacity (liters per minute (LPM) or cubic feet per minute (CFM)), current draw for the motor and controller (Amps) and the voltage signal output from the Analog Device current module (0 to 5V signal). This was done by installing the test equipment according to the following procedure:

1) Prepare the milking system for milking and start the vacuum system with the Digital vacuum gage connected at the test port near the vacuum pump. Record the stable vacuum level (milking vacuum level).

2) Disconnect the vacuum pump piping from the milking system or close the provided valve to the milking system and place an airflow meter in the pipe leading to the vacuum pump or the provided test port.

3) Connect a Digital vacuum gauge to a test port installed in the vacuum pipe in “quiet” air beyond the air flow meter location.

4) Install a Fluke current transformer and multi-meter or DENT power meter on the power input conductor wires in the electrical panel, if possible, or on the conductors leading into the Variable Frequency Drive (VFD) to measure the amperage and/or KW draw of the motor and controller.

The vacuum pump was started with the airflow meter adjusted open. After the vacuum pump was at full speed, the airflow meter was adjusted to maintain the same vacuum level as used during milking (vacuum level measured in step 1). Once the system had stabilized, the current / KW, motor RPM and air flow was recorded. The 0-5 VDC voltage output signal from the Analog Devices’ current module was recorded on a laptop computer using Lab View software. The ABB controller was then programmed to reduce the maximum speed by 100 to 300 RPM and the process was repeated. The full RPM range of the vacuum pump was tested: from 500 to 800 RPM up to full speed (1700 to 2800 RPM).

The voltage signals from the ABB variable speed drive were processed using LabView software by averaging 6 reading together to provide a data point every half second. After the data was imported to an Excel spreadsheet, the voltage signal output from the ABB controller was correlated to the motor speed (RPM), air flow (LPM) and current draw (Amps) using a linear regression analysis.

Milking Time Monitoring Data was recorded from the variable speed drive for one complete milking on four dairy farms ranging from 185 to 430 milking cows. The data set was processed averaging every 6 readings together and then importing the data into an Excel spreadsheet. The main reason for averaging data was to ensure that the data set from a four hour milking would be small enough to fit into an Excel spreadsheet. The equations from the linear regression analysis were used to calculate the average air consumption, current (Amps) or demand load (KW) and the total run time of the vacuum pump. Other data collected included electrical system voltage during milking, number of cows milked, number of parlor stalls/milking units and number of persons involved with milking. From the results, the average air consumption per unit time per milking (LPM/milking unit), parlor turns and cows per hour was determined. Refer to the Appendix for a graph of the air consumption data from each farm.

4

Discussion:The desire of this study was to find a method for estimating energy usage more accurately than a flat percentage, while not requiring the use of any measurements or tools that are not visually available in a walk-through audit. It was assumed that the air consumption per milking unit would be a reasonable predictor.

Data was collected on four different dairy farms, each of which had above average management strategies, milk production in the 22,000 range, and Holstein cows housed in freestall barns. The chart below indicates chosen characteristics of each dairy.

Table 1. Characteristics of four dairies.

Parlor Type No. of

milkingunits

VacuumLevel(kPa)

MotorSize(KW)

PumpCapacity

(LPM)

Hoursper

milkingNo of cows

Milkingsper day

Farm 1 Parallel 2 x 16 44.0 11.18 5593 4 430 3X

Farm 2 Flat Step-up 12 49.1 7.46 2803 3.4 185 2X

Farm 3 Herringbone 2 x 9 44.4 7.46 3568 3.3 278 3X

Farm 4 Parallel 2 x 8 44.0 7.46 4673 4 280 3X

Three of the farms use low line pipelines in parlors while the fourth farm used a high line with their Flat barn, step-up parlor. The control strategy for the variable speed drive on three of the farms involved operating the motor, which is rated at 1750 RPM, at speeds up to 2800 RPM to meet peak demands. The variable frequency drive on Farm 4 kept the motor speed within the motor ratings. All of the farms had 2 people helping with milking chores; one person was milking full time while the second person moved cows and milked. It was estimated that milking labor was approximately 1.5 man equivalent. A time study would be needed to get a more accurate value of milking labor.

Table 2. Performance data of dairies during milking.

No. of units

MilkingAir Flow

(LPM)per unit

MilkingLitresair per cow

Cows per hr

Turnsper hr

WashingAir Flow

(LPM)per unit

Weightedaverageair flow (LPM)

Farm 1 32 35 617 108 3.4 127 43

Farm 2 12 65 863 54 4.5 224 78

Farm 3 18 59 775 84 4.7 133 66

Farm 4 16 25 372 75 4.7 113 28

The air consumption per milking unit for milking ranged from 25 LPM (0.89 CFM) to 65 LPM (2.28 CFM). Farm 4 had very low air consumption per milking unit and therefore the data acquisition was repeated to determine if a measurement error had been made. The vacuum system on this dairy is very tight and the dairyman stresses low air admissions when attaching the milking unit. Farm 2 and 3 were on the high side of the air flow per milking unit, using 65 and 59 LPM air consumption, respectively. The ASAE Standard 518 recommends 85 LPM per milking unit and 1000 LPM for reserve if a unit should fall off. These systems were consuming

5

much of the unit reserve. The cause of such a large range in air consumption per milking unit has not been fully investigated, but vacuum system leakage is thought to be a major factor. Farm 4 had a very tight vacuum system while on Farm 3 several obvious leaks were fixed before testing started. Some milking machine manufacturers have recommended air bleeds to force the vacuum pump to run at a minimum speed to ensure adequate cooling of the pump (usually about 800 RPM). However, none were detected on any of the dairies researched within this study. A system analysis was not done to determine the system leakage during this study. Other calculations in Table 2 such as air consumption per cow showed the same relationship as exists with the air consumption per milking unit.

It would seem probable that the faster the cows are milked, as measured in parlor turns per hour (cows milked per hour divided by number of parlor stalls), the lower the air usage. In Figure 1, the small sample size showed just the opposite trend of what was expected.

Air Consumption vs Parlor Turns

y = 7.8158x + 19.946

0

10

20

30

40

50

60

70

80

90

3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8

Parlor Turns per Hour

Air

Con

sum

ptio

n (L

PM) p

er m

ilkin

g un

it

Figure 1: Air Consumption versus Parlor turns for four dairy farms

Washing air consumption ranged from 113 to 224 LPM with a mean of 130 LPM. The vacuum pump on Farm 2 ran at full speed during the entire wash cycle when the vacuum pump was operating. A weighted average of the air consumption per unit was calculated and ranged from 28 LPM to 78 LPM for the four farms, refer to Table 2.

Energy Consumption

The average KW demand was calculated from the measured amperage and voltage using an assumed power factor of 90%. For 3 phase power, the amperage for one line measurement was multiplied by the square root of 3 to calculate the full amperage. Since pre-audits were not possible on any of these farms, the baseline demand load for the farms had to be estimated assuming they were using a constant speed vacuum pump. The baseline demand load values were estimated assuming the installed motor size would be used for a conventional system. The demand load (KW) prediction was based on a 90% motor load, therefore a 7.46 KW (10 HP) motor will draw 6.7KW and the 11.18 KW (15 HP) motor will draw 10.0 KW under normal load conditions.

6

Table 3 lists the calculated demand loads for milking and washing, the weighted KW average and the assumed baseline KW usage if the system had used a conventional regulator system to control the vacuum level.

The percent savings was calculated as follows:

% Savings = (Baseline KW - Wt Average KW) / Baseline KW

Table 3 - Demand Loads for tested farms.

No. of units

Weightedaverageair flow (LPM)

MilkingKW

Demand

WashingKW

Demand

WeightAverage

KWDemand

BaselineAverage

KW%

Savings

Farm 1 32 43 3.5 7.3 3.9 10.0 61%

Farm 2 12 78 3.5 6.4 3.8 6.7 43%

Farm 3 18 66 3.2 4.8 3.4 6.7 37%

Farm 4 16 28 1.8 4.4 2.0 6.7 68%

Predicted Energy Use

Obviously, this is a small sample size to draw too many conclusions from; more data needs to be taken and differences investigated to increase our understanding. But could the air consumption per unit value provide a reasonable estimation of air consumption for a walk through audit? The average air consumption per milking unit for all farms was calculated at 54 LPM and 62 LPM if Farm 4 is excluded from the average. The air flow rates per milking units of 50, 55 60 and 65 LPM were selected as potential estimates. Table 4 shows the expected average air consumption for each of the farms for the different prediction values.

Table 4: Predicted Air consumption

No. of milking Units @ 50 LPM @ 55 LPM @ 60 LPM @ 65 LPM

Farm 1 32 1600 1760 1920 2080

Farm 2 12 600 660 720 780

Farm 3 18 900 990 1080 1170

Farm 4 16 800 880 960 1040

The variable speed vacuum pump demand load data from all four farms was either calculated from the amperage and voltage measurements or collected from the DENT power meter logger. The assembled data was plotted and a linear regression was applied to the data.

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Vacuum Pump Air Flow versus Demand Load

y = 0.0018x + 1.7729

0.0

5.0

10.0

15.0

0 1000 2000 3000 4000 5000 6000

Air Flow (LPM)

Dem

and

(KW

)

Figure 2: Vacuum pump air flow versus Demand Load

The demand loads (KW) were calculated for each farm for the different potential air flow prediction rates using the linear regression equation from Figure 2. The demand load values are shown in Table 5. An error analysis is shown in Table 6. The goal of a walk through audit is to have the average error of all audits to be zero or slightly positive. However, any particular audit may be off some acceptable percentage. At the bottom of Table 6, the error from Farms 1, 2 & 3 were averaged. Since Farm 4 seems to be an exception it was exclude from the average. From the small sample size it appears that an air consumption rate of 50 or 55 LPM would be acceptable. Since the preference is to be conservative, the 55 LPM (1.94 CFM) rate will be selected.

Table 5: Demand Load with VFD versus Predicted Air Consumption

No. of milkingUnits

@ 50 LPM

KW

@ 55 LPM

KW

@ 60 LPM

KW

@ 65 LPM

KW Actual/Calculated

KW

Farm 1 32 4.6 4.9 5.2 5.5 3.9

Farm 2 12 2.8 3.0 3.1 3.2 3.8

Farm 3 18 3.4 3.6 3.7 3.9 3.4

Farm 4 16 3.2 3.4 3.5 3.6 2.0

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Table 6: % Error - Demand Load with VFD versus Predicted Air Consumption

No. of milkingUnits

@ 50 LPM % Error

@ 55 LPM % Error

@ 60 LPM % Error

@ 65 LPM % Error

Farm 1 32 19 % 27 % 34 % 41 %

Farm 2 12 -25 % -22 % -19 % -16 %

Farm 3 18 0 % 5 % 9 % 14 %

Farm 4 16 61 % 68 % 75 % 82 %

Average error Farm 1,2,3 -2 % 3 % 8 % 13 %

Predicted Savings The original intent was to have a better predictor of energy savings from a VFD versus using a flat percentage. Table 7 shows the predicted savings using an air consumption value per milking unit versus the assumed savings. On two of the farms the energy savings was under estimated, one farm the savings was within 2% of assumed savings and the fourth farm the savings was overestimated by 13%. All of the predictions using 55 LPM per milking unit hovered around a 50% marker of savings. This would indicate that there are more things to consider in making this type of estimate.

Table 7: Predicted Savings versus Assumed Savings

No. of milking Units Baseline KW Predicted KW

Usage% Savings Predicted

Assumed % Savings

Farm 1 32 10.0 4.9 51% 61%

Farm 2 12 6.7 3.0 56% 43%

Farm 3 18 6.7 3.6 47% 49%

Farm 4 16 6.7 3.4 50% 70%

Other Factors that could Affect Air Consumption

Oversized Vacuum Pumps

Several of the vacuum pumps were running slower than the manufacturer’s recommendations due to pump heads that were larger than necessary. The manufacturer's concern is that the pump will not cool adequately due to low air flow which could lead to premature failure. ASAE Standard 518, Milking Machine Installations – Construction and Performance, guideline for vacuum pump sizing recommends a base capacity of 1000 LPM and 85 LPM per milking unit. Table 8 compares the recommended vacuum capacity per ASAE Standard 518 versus the measured vacuum pump capacity.

9

Table 8 – Farm Vacuum Pump Capacity versus ASAE 518 Standard guideline

No of units ASAE guideline (LPM)

MeasuredCapacity (LPM)

% Above Guideline

Farm 1 32 3688 (4720)* 5593 52% (18%)*

Farm 2 12 2020 2803 39%

Farm 3 18 2512 3568 41%

Farm 4 16 2360 4673 98%

* If designed for 2 unit fall-offs.

From Table 8 it can be seen that all systems had excess capacity based on the ASAE standard. The pump on Farm 3 was running well below the manufacturer’s recommend minimum speed because of an extreme excess pump capacity.

Attachment Method

The method of attachment of the milking unit on smaller farms in the upper Midwest tries to achieve minimal air admission during attachment by attaching each teatcup individually where as in large parlor the method often involves holding 3 or 4 teatcups upright, all admitting air, as the teatcups are being attached. To evaluate the effect, the vacuum pump speed was recorded using the method described above while the milking unit was attached, attempting to minimize air admissions and holding 3 teatcups open at one time while attaching the milking unit during several turns of the parlor. Comparing the data showed a 2.5 to 5% increase in air consumption when using the method of applying 3 teatcups at once. Granted, the milker was not accustom to using this method of attachment so the increased air consumption may be higher than a person who uses this method regularly. What is more important from a vacuum pump capacity stand point is that the maximum air consumption required when applying the teatcups 3 at a time increases by 14% to meet the peak air admission rate. Refer to Figure 3 and 4 in the Appendix for sample graphs. The four groups of spikes on each graph represent a period of units being attached with each spike representing one milking unit. All of the test farms were applying teatcups to minimize air admissions.

Milking Unit Effect

In recent years there have been several new milking units introduced to the market that have larger milk hoses and larger diameter short milk tubes. These units have the potential to admit higher flow rates that could effect the total air consumption per milking unit. The air flow rate admitted by these units could also affect vacuum pump guidelines to meet the ASAE 518 Construction and Performance standard. Samples of four milking units sold on the market were tested to determine the simulated fall off air consumption and the air flow through a single teatcup. A milking unit fall-off was simulated by applying vacuum to the unit while it was inverted for approximately 10 seconds. A single teat cup fall-off was simulated by holding the milk unit upright and level with a single teatcup held up as if it were attached to a cow while vacuum was applied to the milking unit. The remaining teatcups were plugged if necessary to keep them from leaking. Two of the claws would be classified as standard claws and two of the claws are recent introductions to the market place with large diameter short milk tubes. None of the claws were equipped with any vacuum shutoff mechanisms on the claw outlet. The units were tested in a working milking parlor connected to a 2000 mm (78”) long, 15.8mm (5/8”)

10

rubber milk hose or a 2000 mm (78”) long, 19.0mm (3/4”) plastic milk hose. The milk hose was connected to a 76.2mm (3”) milk line with a 15.8mm (5/8”) inlet strap-on nipple (16.5mm (0.65”) ID). The vacuum level was 44 kPa (13" Hg). The general characteristics of the units are listed in Table 9.

Table 9: Milking Unit Characteristics

* Claw Body Outlet location Outlet ID Inlet ID Nipple design

Unit 1 - STD Standard Bottom 16.5 mm 9.5 mm BeveledCurved end

Unit 2 - HC Barrel Top 18.0 mm 12.5 mm None

Unit 3 - HC Standard Bottom 15.8 mm 12 mm Blunt End

Unit 4 -STD Barrel Top 15.8 mm 9.5 mm BeveledCurved end

* STD - indicated a conventional claw design, HC - indicates a milking unit with large short milk tube inlets.

A summary of the tests is in Table 10. Large diameter milk hoses have the most affect on air flow rates with an average increase in air flow of 26% and the combination of the large ID inlets on the claw and large milk hoses are additive with an increased air flow of 42%. One of the characteristics of milking units with large inlet diameters is that one open teatcup will admit 75% of the air flow that a fall-off test of the same milking unit will admit versus an average of 46% for a standard claw with a beveled, curved end nipple. This increased air flow through a single teat cup will likely increase the air consumption per milking unit during the attachment of a milking unit and will increase air consumption during fall-off or liner slip events.

Table 10: Affects of large milk hoses and larger inlets on air flow per milking unit

Increased air flow

15.8 mm hose All units

19.0 mm hose All units

Air Flow Difference

2000 mm milk hose 26% 1245 LPM

(44 CFM)

1500 LPM

(53 CFM)

255 LPM

(9 CFM)

Curves beveled ends - standard Units

Large diameter inlet - high capacity units

Milk Inlet nipple types 13% 1200 LPM

(42 CFM)

1320 LPM

(46 CFM)

120 LPM

(4 CFM)

15.8 mm hose & curved beveled nipples

19.0 mm hose & large diameter inlets

Large milk hose and large inlets

42% 1200 LPM

(42 CFM)

1700 LPM

(60 CFM)

500 LPM

(18 CFM)

11

For comparison, the 15.8 mm milk hose without a claw attached had an air flow rate of 1500 LPM while the 19 mm milk hose allowed a flow rate of 2100 LPM. If the milk hose is disconnected directly from the nipple on the milk line, the 15.8 mm ID nipple allowed 2540 LPM of air to flow into the milk line.

ConclusionEstimating the energy consumption of a variable speed vacuum pump using estimated air consumption per milking unit can provide a rough approximation of the energy savings. However, several other parameters need to be investigated in order to increase the accuracy. The system leakage may have been the largest factor that increased the air consumption per unit on farms tested and likely needs more attention on variable speed vacuum systems due to its' implication for reduce energy savings. ASAE Standard 518 states that the allowable leakage should be less than 20 LPM plus 2 LPM per milking unit. There are other factors such as larger long milk hose inside diameter (ID), milking units with large ID inlet nipples and liners with large short milk tubes, milking unit attachment method and vacuum operated equipment such a vacuum detachers. Oversized vacuum pumps will not affect the energy savings significantly unless an orifice is used to admit air into the vacuum system to maintain a minimum pump speed. Future work would need to identify the factors that lead to the large difference in air consumption between the farms.

Acknowledgements

The author would like to extend his sincere appreciation to John and Gary Doerfer, Doerfer Bros. Farm; Brian & Yvonne Brown, Sunshine Dairy; Maier Bros. Farm and Mike Buechel for allowing me to access their dairy facilities in the course of this study.

Disclaimer:Any mention of trade or brand names is done for descriptive purposes only and is not an endorsement or recommendation of the equipment by the author or the University of Wisconsin.

ReferencesAmundson, T.. 2002. Deemed Calculation for Variable Speed Drives on Milking Machine

Vacuum Pumps. May 7, 2002 meeting presentation. Regional Technical Forum, Northwest Power Planning Council, Portland OR. Available at:http://www.nwppc.org/energy/rtf/current.htm. Accessed 2 July 2003.

ASAE Standards, 2001. S518.3: Milking Machine Installations – Construction and Performance. St. Joseph, Mich.: ASAE.

Lee, E.C.. Review of Variable Speed Drive Technology. Wire World Internet, Brantford, Ontario, Canada. Available at: http://www.wireworld.com/seminar/drives/. Accessed 3 July 2003.

Ludington, D.C., D.J. Aneshansley, R.A. Pellerin & F. Guo 1990. Adjustable Speed Drive – Two Vacuum Milking System. ASAE Paper No. 903556. St. Joseph, Mich.: ASAE.

Variable Speed Pump Calculator, Alliant Energy, Madison, WI, Available at http://www.alliantenergy.com/ag/calculator/variable_calc.php3. Accessed 3 May 2002.

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Appendix

Air Consumption - Clean attach

0500

100015002000

1 501 1001 1501Time (1/2 second averages)

Air

Con

sum

ptio

n (L

PM)

Figure 3: Air Consumption during low air admissions attachment

Air Consumption - Sloppy attach

0

500

1000

1500

2000

1 501 1001Time (1/2 second averages)

Air

Con

sum

ptio

n (L

PM)

Figure 4: Air Consumption during high air admissions attachment

13

Farm 1 - Air Consumption32 milking units - Noon milking

0

500

1000

1500

2000

2500

3000

3500

1 5001 10001 15001 20001 25001

Time (1/2 second averages)

Air

Con

sum

ptio

n (L

PM)

0.00

20.00

40.00

60.00

80.00

100.00

120.00

Air

Con

sum

ptio

n (C

FM)

Figure 5: Air Consumption - Farm 1, Noon milking, 32 units

Farm 2 - Air Consumption12 milking units - AM milking

0

500

1000

1500

2000

2500

3000

1 5001 10001 15001 20001

Time (1/2 second averages)

Air

Cons

umpt

ion

(LPM

)

0

20

40

60

80

100

120

Air

Cons

umpt

ion

(CFM

)

Figure 6: Air Consumption - Farm 2, AM milking, 12 units

14

Farm 3 - Air Consumption18 milking units - Noon milking

0

500

1000

1500

2000

2500

3000

3500

4000

1 5001 10001 15001 20001

Time (1/2 second averages)

Air

Con

sum

ptio

n (L

PM)

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

Air

Con

sum

ptio

n (C

FM)

Figure 7: Air Consumption - Farm 3, Noon milking, 18 units

Farm 4 - Air Consumption16 milking units - AM milking

0

500

1000

1500

2000

2500

3000

1 5001 10001 15001 20001 25001

Time (1/2 second averages)

Air

Con

sum

ptio

n (L

PM)

0

20

40

60

80

100

120

140

160

180

Air

Con

sum

ptio

n (C

FM)

Figure 8: Air Consumption - Farm 4, AM milking, 16 units