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Field inspection manual—volumetric measuring devices

Specialized test procedure—Milk receiving and milk pick-up metering systems

Category: Volume
Part: 4-STP
Section: 28
Publication date:
Revision number: 4

Application

Milk receiving metering systems installed at dairy plants and vehicle-mounted milk pick-up metering systems.

There are two approved types of milk receiving systems in general usage:

  • Pressure air elimination systems (type A); and
  • Vacuum air elimination systems (type E).

The fundamental difference between both systems is the configuration of the pump and deaerator.

Pressure air elimination systems (type A) are designed with their suction line connected to the inlet of a centrifugal pump. The outlet of the pump is connected to the inlet of an air eliminator and then to the meter. The air eliminator is maintained under positive pressure during the measurement operation. The transfer point is at the pump, so that the conduit between the pump and the meter remains full at all times during the measurement process.

On vacuum air elimination systems (type E), the air eliminator comes first and is located to have its inlet lower than the product source. These air eliminators are equipped with a liquid level sensor that slows/shuts off the pump and the flow valve when the flow of milk slows or is exhausted. The transfer point is located in the air eliminator. The liquid flow is stopped when the liquid level in the air eliminator reaches a low position. The pump is located downstream from the air eliminator so that the air eliminator operates under vacuum at full flow or low pressure. The meter is located downstream from the pump.

Purpose

The procedure is intended to provide guidance to inspection staff when conducting inspections of the above-mentioned systems. The systems are tested using sanitary bottom loading open neck provers designed for that purpose.

Equipment

Appropriate sanitary volumetric prover dedicated to milk meters (stainless steel bottom fill open neck prover). When selecting the appropriate capacity of proving standard, a minimum test volume should equal or exceed a one-minute run at maximum operating rate.

Note: Proving standards must be verified and designated as a local standard by Measurement Canada. Measurement Canada's mobile prover standards require recertification once every four years. Sanitary milk provers are calibrated to a reference temperature of 4.4 °C and are not to be used for other purposes.

Procedure for testing receiving systems using a volumetric prover

Note: The prover and all associated equipment must be cleaned with vapour / hot water and detergent before use to avoid contamination. Use the plant's clean-in-place system and ensure compliance with dairy sanitary rules.

If the meter is in use when you arrive on the premises, take note of operational pressures and vacuum as well as the flow rate. Tests should cover these conditions. Make sure the flow rate does not exceed the approved capacity.

Walk the downstream lines to check if there are any booster pumps or other components that could change the flow rate or line pressure. When such a component is being used, determine the effect on flow rates, pressure and other conditions. Establish whether the component is required for proper operation and determine the effect on the system when it is not operational, etc.

Examine the system to ensure that it meets the installation requirements referred to in the Notice of Approval.

Obtain an adequate supply of milk to perform the inspection, preferably a full tanker truck compartment containing at least 7000 L for smaller meters. For three inch meters, at least 12 000 L should be available. After each test, for sanitary reasons and to prevent foaming, the milk must be pumped back into the tanker through the truck outlet connection using a special valve assembly. If the reserve of milk is sufficient for all tests, milk can also be directed to the plant tanks.

Install a control valve at the meter outlet to start, stop, and control flow. A second control valve in series with the first is highly desirable in order to duplicate and maintain steady flow rates.

Install a pressure gauge between the valve and the meter to measure back pressure and set flow rates.

Install a vacuum gauge on the suction side of the system, if one is not already there, to monitor vacuum conditions during operation, and to aid in performing a vacuum test.

Install an appropriate hose to divert product from the control valve to the prover inlet valve.

Install the milk return hose to the truck outlet connection.

Connect the metering system receiving hose to the tanker manifold.

If possible, cap the manifold connection to the truck pick-up pump.

Open the truck compartment valve. Wait until foam and air stop venting from the deaerator.

Determine the minimum back pressure which may be reached without exceeding the maximum flow rate for the meter (see silos and booster pumps).

Set the system to the manual mode and start the pump. Open the control valve slowly (the one installed downstream from the meter for the tests). Start milk flowing and fill the system.

Run approximately 500 L of milk to ensure proper system operation.

Perform a vacuum test (consult STP-29).

Perform one test to charge the system and condition the meter chamber. Close prover inlet valve. Open outlet valve and pump prover contents back to tanker compartment. Close prover valve. Turn prover pump off and rinse excess foam through petcock, if necessary.

Drain the prover in accordance with the wet/drain procedure (consult STP-22).

Set the systems to the normal operating mode. Reset register. Open prover drain valve. Start pump, and then open control valve to start test.

Start and stop tests by using the control valve with the pump running. However, do not run the pump excessively with the valve closed. Activate valves in a smooth gradual motion to avoid shock.

Perform at least three fast and one slow test, and print one ticket (consult STP-4, STP-5 and STP-7).

If a compartment runs dry during a test, switch compartments and make one run before resuming tests. Do the same if testing is interrupted.

Perform a product depletion test (consult STP-8).

Leave a copy of the test results with the dairy and place a copy in the log which accompanies the prover.

Interpretation of results

The difference between the normal fast flow test and the product depletion test must not exceed 0.25% of the known test volume. All test results must be within the in-service limit of error prescribed by section 266 of the Weights and Measures Regulations.

Figure 1—Typical milk meter inspection schematic

the long description is located below the image
Legend for figure 1
  • AE Air/vapour eliminator
  • P Pump (truck)
  • M Meter
  • kPa Pressure gauge
    1. Prover loop tie in
    2. Pump off connection
    3. N/A
    4. Prover fill valve
    5. Prover drain valve
    6. Proving loop
    7. Pump (prover)
    8. Truck compartment
Description of Figure 1

Schematic of an inspection point for milk receiving systems. In a typical milk receiving system, a mobile tanker truck is connected to a deaerator from which a main line leads to the milk storage tanks. On the main line, downstream of the deaerator, are a pump, a meter and a pressure gauge. The testing equipment used for the inspection is installed downstream of the pressure gage. A control valve is installed and connected by inlet hose to a prover having inlet and outlet valves. Downstream of the prover's outlet valve, a product return pump and discharge hose are installed so as to return the milk to the mobile tanker truck.

Procedure for testing milk pick-up metering systems using an open neck prover

Note: Currently, there are no milk pick-up metering systems in use in Canada according to the milk marketing boards. The following procedure is retained for further reference and needs to be reviewed and updated before it is used. Volumetric specialists must be consulted. Ensure that the installation complies with the requirements (selector valves, air eliminator) such that the system cannot load products through the meter while unloading product to the feed tank.

Milk pick-up meters must be inspected on the trucks where they are installed. The system may be inspected by simulating a milk pick up by drawing a known volume (500 L) preferably from a prover. The meter alone can be inspected by running product from the truck into the prover. Both of these tests can be performed independent of a dairy's facilities; however, a source of electrical power must be available for the operation of the truck and prover pump.

Determination of the accuracy of the milk pick-up meter

Place truck and prover on level ground.

Install an elbow after the check valve in the metering system to divert metered product to the prover instead of a tanker compartment.

Connect the milk pick-up hose to the pump off connection on the tanker manifold.

Install a hose between the prover inlet valve and the diverter elbow.

Insert milk return hose through tanker compartment hatch from prover product return pump. Do not splash fill. Use drop tube.

Open prover fill valve and close prover drain valve. Open all valves in the metering system including the valve to the full compartment mentioned above.

Reset register and turn pump on. Turn pump off when milk enters prover neck. Start and stop tests with valves open, by using the pump switch.

Close prover fill valve. Turn prover pump on and open prover drain valve at the same time to pump product back to the tanker compartment.

Once prover has drained, close drain valve and turn pump off.

Rinse foam from prover through petcock drain, if required (consult STP-22).

Run at least three normal flow tests to establish the meter's accuracy and repeatability (consult STP-5).

Figure 2—Milk pick-up meter calibration connections

the long description is located below the image
Legend for Figure 2
  • AE Air/vapour eliminator
  • P Pump (truck)
  • M Meter
  • kPa Pressure gauge
    1. Manifold cap
    2. Pump off connection
    3. Milk pick-up hose connection
    4. Prover fill valve
    5. Prover drain valve
    6. Proving loop
    7. Pump (prover)
    8. Truck compartment
Description of Figure 2

Schematic of an inspection point for determining meter error in a milk pick-up system. In a typical milk pick-up system, the mobile tanker truck's tank is connected to the meter through a manifold. Upstream of the manifold's inlet are a control valve, the meter, a pressure gauge, an air eliminator and a positive displacement pump, to which the pickup hose is connected. Downstream of the manifold's outlet is the pump off connection. To determine meter error, the inlet to the manifold is capped and the pickup hose connected to the pump off connection so that the milk will be pumped out of the mobile tanker truck's tank and flow through the air eliminator and meter. The testing equipment used for the inspection is installed downstream of the control valve. The prover is connected to the control valve through the prover's fill valve and a prover pump and product return hose are connected to the prover's drain valve so as to fill the prover, when the fill valve is open and the drain valve closed, and return the milk to the mobile tanker truck's tank, when the fill valve is closed and the drain valve open.

Note: This test evaluates the whole system's accuracy, including its ability to maintain a constant transfer point and to eliminate air entrained into the system.

Place truck and prover on level ground.

Place the prover so that its valves are at the same level and no lower than two metres below the milk pick-up pump.

Connect the truck pick-up hose to one of the prover valves.

Connect another hose between the main tanker manifold outlet connection and the prover pump.

Connect a short hose from the pump outlet to the other prover valve for filling purposes.

Open the valve from a full compartment supplying milk to the prover. Open prover drain valve and turn prover pump on. Shut valve and turn pump off when prover is filled to its nominal value.

Note: If there is adequate gravity head between the milk tanker and the prover, a pump might not be required to fill the prover.

Connect hose from pick-up system to prover valve and zero meter register.

Perform test by using the truck's positive displacement pump. Stop and start tests with valves open by using the pump switch.

Ensure that all metering system valves are open including the compartment valve. Open prover drain valve and turn pump on. Turn pump off when the prover is empty and the meter registration has stopped.

The first test is only for conditioning and priming the system.

Do not disturb pick-up hose between tests.

Close prover drain valves and fill prover again.

Repeat test as required. The pick-up hose should contain the same amount of milk at the end of each test. If not, consider the consequence of variations on test results.

Perform at least two consecutive normal flow tests after priming to assess the effectiveness of the air eliminator and the transfer point.

The contents of the hose may be measured in a graduate along with the drainage from the prover's petcock.

The required priming volume can be established or verified at this time by unloading the prover into an empty system.

Note: Do not attempt slow flow tests because the system operates with a positive displacement pump which cannot be throttled.

Figure 3—Simulation of milk pick up

the long description is located below the image
Legend for figure 3
  • AE Air/vapour eliminator
  • P Pump (truck)
  • M Meter
  • kPa Pressure gauge
    1. N/A
    2. Pump off connection
    3. Milk pick-up hose connection
    4. Prover fill valve
    5. Prover drain valve
    6. Proving loop
    7. Pump (prover) with by-pass
    8. Truck compartment
Description of Figure 3

Schematic of an inspection point for evaluating the accuracy of an entire milk pick-up system, including meter error, capacity to maintain a constant transfer point and ability to eliminate air entrained in the system. In a typical milk pick-up system, the mobile tanker truck's tank is connected to the metering system through a manifold. Upstream of the manifold's inlet are a control and back-check valve, the meter, a pressure gauge, an air eliminator and a positive displacement pump, to which the milk pick-up hose is connected. Downstream of the manifold's outlet is the pump off connection. The testing equipment used for the inspection is installed at the pump-off control valve. A prover and prover pump are connected by hose to the pump-off valve and a product return hose is connected to the milk pick-up connection so as to fill the prover, when the fill valve is open and the drain valve closed, and supply milk in order to test the milk pick-up system, when the prover's fill valve is closed and the drain valve is open.

Revisions

The purpose of revision 4 was to republish the document's graphics.

The purpose of revision 3 was to remove reference to specific test volumes, which were deemed to be inadequately small by the milk industry, and replace it with "known test volume". The name of the test procedure (STP-8) was changed from "Split Compartment / Out of Product Test" to "Product Depletion Test" to standardize terminology. The volume of the required test product to be available for testing three inch meters was corrected to 12 000 L.

The purpose of revision 2 was to add device types 52.10 and 52.20 to the list of device types identified in the title line.

Date modified: