Doc's Corner

    Doc's Corner Article 110-C  

Digimet Accessories

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.

Equipment required:

1. Digimet
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 both ends
- 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 both ends
- One - 4 to 6 inch 7/8 milk hose
- One - 4 to 6 inch 5/8 milk hose

QVST testing apparatus, plus calibrated caps

Testing procedure:

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 QVST apparatus.
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 reduction.