AIRFLOW MEASUREMENTS AND REQUIREMENTS FOR TODAY'S MILKING
SYSTEMS (CMFBMP DAIRY GUIDELINES) .
A milking system with INSUFFICIENT airflow capacity at the vacuum
pump or with INADEQUATE vacuum line sizing and plumbing between the
vacuum pump and the milk receiver jar WILL ADVERSELY AFFECT BOTH
UDDER HEALTH AND PEAK MILK PRODUCTION.
The article reviews some of the common terms that may be used to
describe the airflow capacity and airflow characteristics of your
milking system. Basic formulas for determining airflow requirements
for any system are also included.
The accepted standard units for measuring and expressing airflows
within a milking system are Cubic Feet per Minute (or CFM)
and Litres per Minute (or L/min).
CFM may be expressed two different ways. One way is known as the
American Standard - commonly denoted as ASME which stands for
the American Society of Mechanical Engineers' Standard. The second
way is known as the New Zealand Standard - commonly denoted
as N.Z.
It makes a big difference to know which Standard is being used
when discussing airflow levels since 1.0 CFM ASME = 2.0 CFM N.Z.
If in doubt, always ask to confirm which Standard system is being
used to express airflow.
The conversion between CFM ASME and L/min ASME is as follows:
Airflow is measured using a device known as an airflow meter (AFM).
Various makes, styles and capacities of AFMs exist. Airflow
sensitivities and capacities vary among AFMs from a low of 1 to 2
CFM ASME to a high of where total airflow capacity exceeds 200 CFM
ASME.
AFMs may be used to measure and compare a vacuum pump's actual
airflow capacity against its rated capacity according to
manufacturer specs. Other uses might include determining the degree
of airflow loss due to system air leaks and/or restrictions in the
plumbing of vacuum lines throughout the system. AFMs also play a key
role in evaluating vacuum regulator performance as part of a
complete or dynamic system analysis. The vacuum level at which AFM
readings are collected will vary with the specific test being
performed.
AFM users must follow manufacturer recommendations on the proper
use and collection of airflow readings or else serious measurement
errors could result. Proper positioning of the AFM, proper selection
of test port size and proper selection of AFM adapter size are a few
of the critical operational areas that the user must be aware of.
A general rule of thumb for estimating the airflow capacity of
a vacuum pump in cfm ASME at 15.0 inches of mercury (in.Hg.)
vacuum is to take the horsepower (HP) rating of the pump motor and
multiply it by 10.
The following formulas are currently recommended for estimating
the airflow capacity requirements for any sized milking system
(Note: Read the caution note following the formulas. If you have a
question, call your dealer or me at 204-945-7670).
- Formula for estimating required vacuum pump airflow capacity
at normal system operating vacuum: *Required vacuum pump capacity
= 35 CFM ASME (base) + 3.0 CFM ASME per milking unit.
- Formula for estimating effective reserve (ER) airflow
requirements for any system with up to 80 milking units at normal
system operating vacuum: *ER = 35 CFM ASME (base) + 1.0 CFM ASME
per milking unit.
- No milking system should have less than 35 CFM ASME of ER nor
require more than 120 CFM ASME of ER to properly clean or milk.
CAUTION: NEVER INCREASE THE AIRFLOW CAPACITY OF ANY
MILKING SYSTEM WITHOUT FIRST HAVING THE WHOLE SYSTEM EVALUATED TO
ENSURE IT IS PROPERLY PLUMBED, SIZED AND DESIGNED TO HANDLE THE
EXTRA AIRFLOW OF AN ADDITIONAL OR LARGER VACUUM PUMP.
PLEASE NOTE: Insert this article under the MILKING SYSTEMS
section in your white Farm Business Management Guidelines for Dairy
binder that you received this year.
For further information contact:
Tom Droppo, B.Sc.(Agr.),M.Sc., P.Ag., C.I.M. Manitoba
Dairy Specialist Animal Industry Branch, Manitoba Agriculture
Telephone: (204) 945-7670 Fax: (204) 945-4327
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