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Publication #DS3

Requirements of a Milking System 1

David R. Bray2

Vacuum requirements

The amount of vacuum used to operate the milking system is quite small, less than 2 CFM per unit. Extra CFMs are needed to compensate for vacuum losses that occur naturally in the system: head loss and resistance of pipes, elbows, etc. Thirty CFM ASME are needed in any system just to keep the system operating.

Leaks account for a 10% loss (the difference between pump CFMs and system CFMs). Milk meters, unit slippage, air leakage used when applying the unit, and unit fall-off also consume varying amounts of vacuum depending on the skills of the operators.

Stated vacuum requirements vary greatly and are based on personal bias rather than research. The usual method is expressing CFMs per unit, which usually undersizes small systems and greatly oversizes large systems.

Electric motors that run vacuum pumps are usually either 5, 7.5, 10, 15, or 20 HP and 1 HP motors will deliver 10 CFM ASME on an oil pump, or 7.5 CFM on a water pump. You must determine the pump size for your vacuum usage range. For determining the size of vacuum pump needed, include 30 CFM for running the system, 10 percent loss due to leaks, and 3 CFM per unit for each unit (2 CFM to milk and 1 CFM added for milk meters and other losses) (see Table 1 , Table 2 , and Table 3 ). This should provide more than adequate vacuum for most systems. This does not include extra capacity for one half of the units open on the floor. A milking system should not be designed for poor milking procedures. Adequate milking vacuum level to prevent liner slip will reduce fall-offs and most automatic take offs will shut off automatically on fall-offs.

Table 1. 

Florida vacuum system requirements.

1. 30 CFM ASME to run the system.

2. 10% leakage in the system.

3. 3 CFM/unit, including milk meters and usage losses.

Pump HP

Oil Pumps*

Water Pumps*

5

50

-30 to run system

-5 leaks

15 for units/3/unit = 5 units

38

-30 to run system

-4 leaks

4 for units/3/unit = 1 unit

7.5

75

-30 to run system

-7.5 leaks

37.5 for units/3/unit = 12 units

56

-30 to run system

-6 leaks

20 for units/3/unit = 6 units

10

100

-30 to run system

- 10 leaks

60 for units/3/unit = 20 units

75

-30 to run system

-7.5 leaks

37.5 for units/3/unit = 12 units

15

150

-30 to run system

-15 leaks

105 for units/3/unit = 35 units

113

-30 to run system

-11 leaks

72 for units/3/unit = 24 units

20

200

-30 to run system

-20 leaks

150 for units/3/unit = 50 units

150

-30 to run system

- 15 leaks

105 for units/3/unit = 35 units

*Numbers expressed in CFMs unless otherwise stated.

Table 2. 

Pump horsepower and number of milk units.

HP

No. Units with oil pumps

No. Units with water pumps

5

1 - 5

1

7.5

6 - 12

2 - 6

10

13 - 20

7 - 12

15

21 - 35

13 - 24

20

36 - 50

25 - 35

Table 3. 

Parlor size and size of pump needed (one unit per stall).

Size of Parlor

Number of Units

Oil Pump HP

Water Pump HP

Double 6

12

7.5

10

Double 8

16

10

15

Double 10

20

10

15

Double 12

24

15

15

Double 16

32

15

20

Double 20

40

20

25

Double 30

60

25

30

Double 40

80

40

50

Milk Line Size

Research has indicated that milk lines have been oversized in the past. Oversized lines are expensive to purchase and expensive to clean, because they require more hot water and chemicals. See Table 4 from the 1993 Proceedings at the National Mastitis Council for the new recommendations.

Table 4. 

Number of units per slope.a

Milk Line Size

% Slope

0.5

0.8

1.0

1.25

1.5

2.0

2 inches

2

3

3

4

4

5

2.5 inches

4

5

6

7

8

10

3 inches

6

9

10

13

16

24

4 inchesb

21

28

32

35

38

43

aParlor, with units attached every 10 seconds per slope.

Peak flow rate = (12 lb/min)/cow

Steady air admission = (0.35-0.7 scfm)/unit

Transient air admission = (3.5 scfm)/slope

bNumber per 4" line may vary with number of operations.

Pulsator Line Size

A 3-inch diameter plastic pulsator line is used for rigidity and ease of taping for pulsators. There is no need for a size larger than 3 inches.

Vacuum Controllers

Type - diaphragm type are the most common and sensitive - Sentinel, Westfalia, Delaval Servo, DEC Servo, etc. Dead weight controllers should be avoided.

Location - In as clean an environment as possible and also easily accessible for cleaning. The vacuum controller should be located where the manufacturer recommends, usually between pump and the trap. If located on the balance or reserve tank, the diaphragm type should be double elbowed off the tank.

Maintenance - Clean as often as recommended or at least once a month. In systems with excessive amounts of pump capacity, cleaning must be carried out more often.

Pulsators

A pulsation rate of 40-60 pulsations per minute is adequate. Pulsation ratios of between 50:50 and 70:30 are adequate. A 70:30 ratio with 60 pulsations per minute gives the fastest milking. Alternate and simultaneous types are both acceptable. The choice of pulsation rates, ratios and type are more a matter of personal choice than based on any scientific data. Those commonly available from manufacturers work well. Pulsators should be cleaned monthly. Dust caps more often if dust, moisture and insects are common in the area.

Line Vacuum Level

Vacuum levels used are more based on choice than fact, as any vacuum between 12" Hg and 15" Hg may be adequate. Most high lines milk better at 15", low lines may work at 13.5" Hg. For maximum milking speed (high or low line) milk at 15" vacuum, 60 pulsations per minute, 70:30 ratio. But if "liner slip" or "fall off" are a problem, raising the vacuum to 15" usually helps. Vacuum levels above 15" Hg should be avoided. Line vacuum should be checked at the pump, the receiving jar, and by the controller.

Differences in vacuum levels between pump and receiver should be less than 0.5"Hg. Higher readings, indicating greater pressure drops, relate to decreased CFM at receiver. Greater pressure drops are influenced by small line sizes, excessive elbows, or unreasonably high air flows.

Differences in vacuum levels between receiver and controller should be less than 0.2" Hg . Higher readings indicate higher vacuum differences which influence controller performance.

Footnotes

1.

This document is DS3, one of a series of the Animal Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date February 1996. Revised June 2003. Reviewed February 2012. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

David R. Bray, Extension Agent III, Milking Management and Mastitis, Dairy and Poultry Sciences, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.