The information contained in these web pages has not been verified for correctness. Some of the information contained herein is hearsay and may not be correct. Use the information from these pages only at your own risk!

Milking Equipment

The milking machine is the most important piece of equipment on the dairy farm. It is used more often and more hours per year than any other piece of equipment, including the farm tractor.

Machine Components

There are five basic components of the milking machine: the vacuum pump, vacuum controller or regulator, pulsator, teat cup shell and teat cup liner or inflation. Other parts of the system such as the balance tank, lines, vacuum gauge, sanitary trap, etc. are accessories to these main components.

Vacuum pump:

The function of the vacuum pump is to remove air from a closed system, thereby creating a partial vacuum. Atmospheric air creates a pressure on all surfaces, and when measured with a manometer will cause mercury to rise in a column to 29.92 inches at sea level. This is called barometric pressure. The vacuum pump creates a partial vacuum by removing most of the air from a closed system, thus reducing the pressure of the air. The difference between the almost 30 inches of mercury at atmospheric pressure and the reduced air pressure is the vacuum created and is expressed in inches of mercury.

The size of the vacuum pump is usually expressed in terms of cubic feet of air removed from the system per minute (CFM). The CFM rating of vacuum pumps is measured in one of two ways: The ASME Standard (the pump ratings designated by the American Society of Mechanical Engineers and adopted by the Milting Machine Manufacturers' Council of the Farm Equipment Institute); and The New Zealand Standard.

The two methods measure the volume of air at different pressures. The American Standard is based upon the volumetric delivery rate at normal atmospheric pressure of about 30 inches of mercury, while the New Zealand Standard is based upon the volume of air delivered at the reduced pressure of 15 inches of mercury. Two volume units of air at 15 inches of vacuum (1/2 an atmosphere) equal one volume unit of air at atmospheric pressure. Thus, 1 CFM ASME Standard = 2 CFM New Zealand Standard. Boumatic and Surge pumps are rated by the New Zealand Standard, while the ASME standard is used to rate the pumps of most other companies.

The CFM required to operate a milking installation depends upon the amount of air introduced into the vacuum system, which in turn depends on the number of milker units used, the size of the milk and vacuum lines, the number and sizes of auxiliary milking equipment such as weigh jars and milk metering devices, the amount of air leakage into the system, and the efficiency of the operator. If there are vacuum operated accessories such as doors and gates, a separate system should operate them.

Current recommendations for vacuum pump size needed are based upon research in Pennsylvania and New York. They are shown in the following tables:

For stall barns with pipelines and parlors with swing units.

Number of Units Pump CFM (ASME) Capacity
2 36
4 42
6 52
8 66
10 80

For parlors with milker units at each stall.

Number of Units Pump CFM (ASME) Capacity
6 48
8 56
12 78
16 100
20 112
24 120

While these tables are helpful in determining vacuum pump size needed, the critical value needed in a system is the reserve air capacity. With all the equipment set-up ready to milk, there should be between 3 and 5 cfm (ASME) reserve air per milker unit.

The vacuum pump and the power unit should be installed as close as possible and practicable to the milking area. Such locations as a feed room or near a haymow chute should be avoided. The exhaust from the pump should be piped to the outside of the building through a pipe whose diameter is at least as great as that of the pump's intake port. Mufflers or silencers should not be used, since they reduce effective pumping capacity. On some pumps, mufflers may perform other functions such as filtering or reducing theoil film, which may be exhausted with the air. Since oil is present in most exhausts, the exhaust should be directed downward and away from the side of the building. This prevents rain water from entering the exhaust pipe and pump, and also prevents accumulation of oil and dirt on the side of the building.

Servicing the pump should be performed as directed in the service manual. Maintaining the oil level in the pump or supply cup and checking the belt for proper alignment and tension are the two most important maintenance procedures. These should be done every two weeks. Recommended annual or semi-annual service checks will vary with the pump and the manufacturer's specifications.

Vacuum controller (regulator):

The vacuum controller admits air into the milking system to maintain a set maximum vacuum on the pulsator and milk lines. The CFM rating of the controller must be equal to or greater than the vacuum pump capacity. A controller that is too small may result in an excessively high vacuum level which could cause damage to the teats.

Weight-type regulators usually do not provide the vacuum stability desired. They should be replaced with the newer style regulators available.

Controllers should be installed in a clean area where moisture and dirt will not affect their proper operation, and where they will not freeze in cold weather if condensation accumulates in them.

Vacuum controllers should be located between the cow and the pump. In the bucket milking system the controllers should be placed between the pump and the first stall cock opening. In the pipeline system the controllers should be placed between the vacuum pump and the trap. Controllers are often located near or on the vacuum reserve tank. Some people think controllers should be located as close to the cow as possible. By Ohio Health Department regulation, the closest point the controller can be located to the milk line side is at the sanitary trap. For this reason, locate the trap and receiving jar as close to the cow as possible. Locate controllers where the air admitted into them is relatively clean. Easy accessibility is important for routine observation and maintenance.

Controllers are not needed on the pulsator line, if the pulsator line is fully looped to the balance tank and the controllers are mounted on the tank. If there is a controller on the pulsator line, it should control the vacuum level at the same level as the controllers on the milk line. Different vacuum levels on the two lines is an imbalance that should be avoided.

Check and clean the controller at least every two weeks. Accumulation of dirt in the valve is one of the primary causes of malfunction. The manufacturer's recommendations for maintenance and service should be closely followed.


The function of pulsators is to alternate the space between the teat cup shell and teat cup liner between a partial vacuum (milking phase) and atmospheric air pressure (rest phase). During the milking phase, the space between the inflation and shell, and the space inside the inflation have the same partial vacuum. This causes the inflation to open and milk to flow from the teat. Milk flows from the teat because the pressure inside the udder is greater than that outside the teat end.

During the rest phase, air at normal atmospheric pressure,enters between the shell and inflation. Due to the partial vacuum inside the inflation, the inflation collapses around the teat. The pressure of the collapsed inflation helps massage the teat, preventing congestion of blood and body fluids in the teat skin and tissue.

The number of times per minute that the pulsator alternates between the milking and rest phase is called the pulsation rate. Rates vary from about 40 to 80 pulsations per minute, depending upon the manufacturer. A rate between 50 to 60 is recommended.

The ratio of time the inflation is in the milking phase to the time it is in the rest phase is called the pulsation ratio. Ratios vary by manufacturer, from 50:50 to about 70:30. Cows will usually milk slightly faster with a wider ratio. However, the longer milk phase and shorter rest phase may cause teat end trauma and damage if the milking equipment is not working properly and good milking practices are not followed. Ratios closer to 60:40 are less likely to contribute to problem situations.

The closing patterns of the inflations varies by manufacturer. Some have all four inflations of a claw closing at once (simultaneous), while others have an alternating pattern (only two inflations close at a time). The alternating pattern results in less claw flooding in units with a small claw. In units with larger claws that do not flood, alternating pulsation is not as important. Claw flooding (filling) is not desired, for it causes vacuum fluctuation at the teat end. This, in turn, can result in teat end injury and the back flushing of milk into the teat. The introduction of mastitis causing organisms into the udder can occur in such a situation.

Pulsators are controlled either by electricity or air (pneumatically) or a combination of the two. Electrically controlled units are preferred because of their more consistent action. Pneumatically operated units are more unreliable and require more maintenance. It is recommended that when four or more units are being used, the electric pulsators be wired on two or more circuits to prevent them from being in the same phase. This can help prevent cyclic vacuum fluctuations on the pulsator line.

A new type of milking unit from New Zealand has the pulsator mounted directly on top of the claw. It operates by vacuum and not by air or electricity. At this time, research studies evaluating the units are lacking.

Teat cup shell and teat cup liner (inflation):

These two components form the pulsating chamber which allows milk to be removed from the teat. The shell size used should correspond to the inflation size. Most companies recommend the use of narrow bore liners (3/4 inch or less in internal diameter). They have less tendency to climb the teats, especially towards the end of milking, which can shut off milk flow from the udder into the teats and can also cause udder trauma at the base of the teats. Special types of inflations having features such as being square, having ribbed sides, or special kinds of tops have not been evaluated in controlled experiments. Many dairymen have used them successfully.

Air inlets are available to admit air into the tail piece of the liner (vented inflation). This is done in an attempt to avoid claw and tail piece flooding with milk. Most manufacturers have attempted to control claw flooding by admitting air into the claw. Vented inflations may cause problems in systems that have inadequate reserve air flow. Observations also indicate that inlets are not satisfactory when used in liners with a high collapse differential. While many dairymen are successfully using vented inflations, objective information for recommending their use is lacking. If they are used, the air inlet in the claw should be closed.

Research in New Zealand and Germany is in progress to design and develop a milking claw without inflations. Perhaps such a unit will be perfected and available in the future.

Interconnecting Parts and Their Relationship to Machine Function

Claws: Claws should be of adequate size to avoid flooding. Most claws admit air to aid in preventing flooding. Claws or breaker cups should not have filters. Be sure the ferrules (tubes where the liners are attached to the claw) are not bent or damaged. If they are, blockage of milk flow from the teat cup can occur, resulting in slow milking and teat irritation.

Long Milk Hose: Be sure the long milk hose is in good condition, does not leak, is not too long and does not contain a filter. Do not let it hang lower than the cows udder before elevating it, or do not elevate it before dropping into a low line or weigh jar.

Milk Inlets: Place milk inlets on the upper half of the line. This prevents them from being covered with milk, which can cause undesired vacuum fluctuation.

Milk Line: Place milk lines below the cows udder so that milk is not elevated. If weigh jars are used, a low line is not necessary. Low-lines allow for less claw and milk hose flooding during peak milk flow. This in turn reduces vacuum fluctuation, which can cause teat-end erosion, slow milking and perhaps predispose cows to mastitis. The line should be of adequate size for the number of units and the number of inlets into the receiving jar. Loop all milk lines to the receiver jar. Recommended line sizes are as follows:

Number of Units Number of Units
Size of Milk Line Single Slope Double Slope
11/2 inches 2 4
2 inches 4 8
21/2 inches 6 12
3 inches 9 18

All milk lines should be sloped 11/2 inches per 10 feet to the receiver jar. Milk lines of three inches or larger may be difficult to clean properly. Therefore, a looped double sloped line of smaller diameter is often preferred. Milk lines can either be glass or stainless steel. Stainless steel is preferred because of its durability. Most stainless steel lines are welded on the job and joined with sanitary connections or clamps and gaskets.

Pulsator or Vacuum Line: The pulsator line should be of adequate size and looped into the balance tank. It should be cleaned regularly. Galvanized or PVC pipe can be used. The PVC pipe creates less friction and is preferred. Line sizes recommended are as follows:

Number of Milking Units Pipe Size
2-12 2 inches
more than 12 3 inches

Receiving Jar: Install receiving jars with an adequate number of ports. For example, a double slope system will have two ports. Some installations use a "T" to allow milk from two lines to enter through a single port. This is not recommended. The valve between the receiving jar and the milk pump should not admit air. If a bubbling action occurs in the receiver jar, air is leaking past the valve and it should be replaced.

Vacuum Balance Tank: The balance tank is sometimes referred to as a vacuum reserve, air distribution, or a header tank. It is used for several purposes. First, it is a point of entry for header pipes leading to the pump(s), to the trap and to the pulsator line. In this regard, it is a distribution tank. It also represents a volume which when evacuated has a cushioning effect on vacuum levels when small amounts of air and milk are admitted. In this regard, it is a cushion tank. If oversized it may be used as a reserve tank to compensate for inadequate pump capacity. This, however, leads to slow recovery time and irregular fluctuations. A tank size of five gallons per milking unit is commonly used. If air is admitted to a container under vacuum, vacuum level will fall unless air is removed. Thus, adequate pump capacity and reserve air flow are important in maintaining a stable vacuum. A properly installed balance tank is the best site for locating regulators to avoid unequal vacuum levels in the milk and pulsator lines.

Traditionally, the balance tank has been located directly under or right next to the vacuum pump. This has been and continues to be satisfactory for smaller installations, providing the pump is not too far from the milking area. For larger installations (double-8 herringbone or larger), it is recommended that the balance tank be located as near the milking units as possible. This location gives the most stable vacuum to systems requiring large amounts of air movement. Locating the tank horizontally over the receiver jar and sanitary trap or over the parlor gets the vacuum reserve as close to the milkers as is practically possible. The vacuum regulators should be placed on the top or side of the balance tank.

Rubber Components: All rubber components need to be replaced at regular intervals. With inflations and milk hoses, this is essential for sanitation. Replacement is essential for all rubber parts if small leaks with a large cumulative effect on fluctuation are to be avoided.

Weigh Jars: Weigh jars are glass jars calibrated to weigh the volume of milk accurately. They are used in milking parlors by some dairymen for the following reasons:

  1. Abnormal milk secreted by some cows can be isolated and discarded.
  2. The daily production level of each cow can be checked.
  3. They assist in stabilizing the vacuum on the teat end.

This is especially true where the milk line is located above the level of the udder. Weight jars should be placed so the milk inlet ports are about the same height as the cows' udders. This reduces the lifting of milk from the udder which can cause teat end vacuum fluctuation.

Weigh jars also have certain disadvantages:

  1. Emptying the weigh jar after each cow can slow down the efficiency of the parlor.
  2. They tend to congest a parlor pit and reduce ease of operator movement.
  3. They are fairly expensive to purchase and replace if broken.

Most weigh jars are approved for use in the DHIA production testing programs.

Sanitary Trap: The sanitary trap is usually located close to the milk receiver jar. Its purpose is to trap any milk or wash water that goes past the receiver jar so it doesn't enter the vacuum balance tank or pump. The pipes connecting the trap with the balance tank and receiver jar should be the same size as the milk line, and should slope toward the trap.

Machine Function Guidelines

Vacuum Fluctuation: Vacuum fluctuations at the teat end should be minimal. However, no one has definitely established this minimum figure. McDonald from the National Animal Disease Lab suggests that the vacuum fluctuation at the teat end should never exceed two inches of mercury.

Fluctuations can occur in both a cyclic and irregular pattern. A cyclic pattern of fluctuation is related to pulsation and milk flow. This cyclic pattern may be affected by other forces, but the predominant effect is produced within the machine. Rapid flow of milk and flooding at the teat end cause most of this type of fluctuation. Irregular fluctuations are unrelated to pulsation. They are mainly caused by inadequate air movement or transporting milk with air, as is necessary in a high line system or in a system with a riser. Milk lines of inadequate size, or with inadequate slope, can flood and cause irregular vacuum fluctuation. They may also be related to poor milking technique in attaching and removing milkers. Vacuum fluctuations have been demonstrated to increase the rate of new intramammary infections (mastitis). There still remains some speculation about the way this happens, but from a practical standpoint, eliminating fluctuations can be beneficial to mastitis control. The following is a list of factors involved in vacuum fluctuation.

  1. Inadequate pump capacity.
  2. Inadequate reserve air flow (vacuum reserve).
  3. Flooding.
  4. Other obstruction to air flow.
  5. Leaks in the system.
  6. Simultaneous pulsation in machines with minimal claw capacity.
  7. Use of milking vacuum to elevate and transport milk.
  8. Inadequate regulator function.

Vacuum Level: Most milking machines operate with 11 to 15 inches of vacuum. Many knowledgeable workers in the field recommend a vacuum level of between 11 and 13 inches of mercury. It is common to find systems that operate at much higher vacuum levels than originally designed. Farmers often interfere with regulators to achieve a higher vacuum level, which compensates, in an adverse way, for inadequate vacuum reserve. Inadequate vacuum reserve occurs commonly with inadequate pump capacity, ageing of the system with development of leaks and when additional units are added.

Vacuum guages may lose their accuracy with time. They should be recalibrated or replaced yearly. It is recommended that a mercury column, which measures vacuum level of the milking system, also be installed. Mercury columns are available from all milking equipment manufacturers.

Adequate Massage: Although it is commonly accepted that a milking machine must adequately massage the teat end, it is not clear what constitutes adequate massage. With this lack of precise information, general recommendations are to keep the pulsators in good operating condition, minimize flooding of the teat cup liners, and have the same vacuum level on the inside and outside of the teat cup liners. McDonald has suggested that the massage force range from 6 to 11 inches of mercury vacuum.

Flooding: When milk completely fills any tube or line between the teat end and the vacuum pump, the system is said to be flooded. Placing a solid column of milk in the air column slows its movement. If air is being admitted to the system behind the column of milk, the vacuum level will lower. Some researchers feel that flooding alone is detrimental and vacuum fluctuation is secondary in causing new udder infections. Their opinion is based on the possibility of milk from an infected quarter mixing in the flooded claw and then contaminating the teat end of an uninfected quarter. This is a possibility. One researcher showed that impact forces on a teat end do occur when the liner opens. The following is a list of factors involved in flooding.

  1. Fast milking cows.
  2. Fast milking machines.
  3. Liner tail piece of inadequate capacity.
  4. Small Claws and wide ratios.
  5. Elevating milk with milking vacuum.
  6. Milk line too small for number of milkers.
  7. Inadequate milk line slope.
  8. Risers.
  9. In line milk filters.
  10. Elbows in milk line.
  11. Improperly placed milk inlets.

Machine and Equipment Maintenance

Because the milking system is used daily, it needs to be serviced and maintained in proper working condition. Some items need to be checked more often than others. An example of a maintenance check list to use follows:

Daily maintenance checks to make (at each milking)

  1. vacuum regulator operating properly
  2. vacuum level at desired level
  3. no breaks in inflations and hoses
  4. vacuum pump oil level satisfactory
  5. pulsators operating properly
  6. air inlets into claw or inflation tailpiece are open
  7. bulk tank turned on and operating properly

Checks to make every few weeks

  1. clean vacuum regulator
  2. check belt tension on vacuum pump
  3. disassemble pulsators and check for wear
  4. cheek lines, couplings and inlets for leaks
  5. inspect, rotate or change inflations if needed
  6. inspect CIP system for proper cleaning
  7. check water temperature after circulating through system—it should be above 110 F

Checks to make every six months to one year

  1. reserve air capacity of system
  2. graph pulsator action
  3. vacuum gauge for accuracy
  4. all electrical connections
  5. replace hoses and rubber parts as needed
  6. valve in receiver jar for air leak
  7. stray voltage level while milking
  8. water quality and chemicals used for cleaning
  9. all other service checks as specified by the manufacturer

By following a regular maintenance schedule, the dairyman can milk efficiently and can reduce the role of the milking machine as a factor in predisposing cows to udder infections.

Machine Malfunction Checklist

Even with routine maintenance of the milking equipment by the dairyman and the machine company serviceman, machine malfunction can occur. Listed below are some common problems that may occur and suggested corrective action.

Inadequate vacuum or vacuum fluctuation

Pump too small -- Replace (reserve should be 50% of pump capacity).

Plugged line -- Clean with lye once a month.

Sticky vacuum regulator -- Clean and oil, adjust if necessary.

Worn belt -- Replace.

Worn pump -- Repair or replace.

Air leaks -- Tighten couplings, repair or replace gaskets or stallcocks.

Broken vacuum line -- Replace.

Vacuum or milk lines too small -- Replace.

Pump running too slow -- Have serviceman check voltage and pulley sizes.

Too many milking units -- Eliminate units or get larger system.

High Vacuum

Sticky or dirty vacuum regulator -- Clean and oil regularly.

Too much weight on regulator -- Remove and adjust weights.

Pulsators too fast or too slow

Poor adjustment -- Correct to manufacturer's recommended rate.

High or low vacuum -- Adjust to manufacturer's recommended pressure.

Dirty pulsators -- Clean at least once a month.

Worn pulsators -- Repair.

Teat cup inflations

Ballooned, cracked or blistered -- replace entire set of four.

Rough -- Clean thoroughly.

Teat cups drop off

Pipeline couplings may leak, valves not properly seated, or poor air tube or hose -- Tighten couplings or replace gaskets, valves or hose.

Plugged air-bleeder vents -- Clean daily.

Inadequate vacuum -- See above.

Too many milking units -- See above.

Milk line too high -- See above.

Slow milking

Inflations in poor condition -- Replace.

Air tubes contain holes -- Replace.

Plugged air-bleeder vent -- Clean daily.

Inadequate vacuum -- See above.

Poor pulsation -- Clean and service pulsator.

Pipeline not washing

Water may not be hot enough -- Check hot water heater and water pressure.

Washing detergent solution too weak -- Add more detergent to washing cycle, use recommended amount.

Wrong type of cleaner -- Use total program with one manufacturer's products and use as recommended.

Related web pages:

Commercial suppliers:

Electronic mailing lists:

Suggested references:

If you are interested in any of the titles below, click on the title and it will take you to Amazon.com for ordering. Click on the icon at the left for more information.


This page was last updated on November 16, 2002