Corner Article 110-C
Quick Vacuum Stability Test (QVST)
The Quick Vacuum Stability Test is for evaluating performance of
milking vacuum systems while the milking system is in use.
2. QVST testing apparatus
- Four calibrated air holes (20 cfm, 40 cfm, 80 cfm and 120 cfm)
drilled into four steel caps (approx. CFM flows at 12
to 13 inches)
- One - 1 inch metal quick-close valve with internal threading
- One - metal adapter - one inch pipe threads one end and 3/4
hose slip at other end
- One - 4 inch stainless threaded pipe nipple 1 inch threaded
- One - 4 to 6 inch 7/8 milk hose
- One - 4 to 6 inch 5/8 milk hose
QVST testing apparatus, plus calibrated
(Note: milk hoses
1. Attach the Digimet testing hose (30 to 50 feet length) to a
test point nipple at either the receiver area or the first milk
valve from the receiver.
2. Move into the milking area 30 to 50 feet with Digimet and the
3. Attach QVST apparatus to milk valve within the 30-50 foot
area (make certain milker leaves this milking unit unattached)
using the 7/8 milk hose nipple to either a 7/8 or a 3/4 milk
outlet or by slipping a 5/8 milk hose nipple into the 7/8 milk
hose nipple for a 5/8 milk inlet nipple.
4. Re-set Digimet in vacuum mode.
5. With the 20 CFM cap attached to QVST apparatus quickly open
and close valve at count of 4 seconds, repeating until vacuum
fluctuation reading within several 100ths - store in slot 1 of
Digimet and repeat same procedure with each cap until four slots
are filled in Digimet storage
Interpretation of Digimet readings:
In my opinion after many hundreds of vacuum system evaluations,
the following performance data suggest a proper performing
milking vacuum system if fluctuation ranges fall within the
parameters indicated above:
- 20 CFM -4 second leak - 0.25" - 0.40" Hg fluctuation
- 40 CFM - 4 second leak - 0.41" - 0.65" Hg fluctuation
- 80 CFM - 4 second leak - 0.66" - 1.00" Hg fluctuation
- 120 CFM -4 second leak - 1.01" - 1.50" Hg fluctuation
As long as monthly testing in this manner fall within these
ranges the milking vacuum system remains acceptable - once
variations are observed, the milking vacuum system must be
evaluated using more thorough procedures.
Developed by: Western Dairies, Inc.
Research and Development - Lionel H. Brazil DVM
Doc's Corner is a contribution of Lionel H. Brazil, DVM
(1928-2007). Dr. Brazil offered dairy consultation
services worldwide for many years. His services covered the following areas: milking management, vacuum system evaluation; and all management procedures relating to mastitis control and SCC