Dairy Establishment Inspection Manual – Chapter 18
D. Pressure differential

This page is part of the Guidance Document Repository (GDR).

Looking for related documents?
Search for related documents in the Guidance Document Repository

Test 19: Pinholes Check - Dye Recirculation Procedure

Note: Other effective tests (e.g. spraying dye, Freon method, helium test, pressure method, Testex Procedure) are also acceptable. For other effective tests used, the establishment must have validated written procedures.

Application:

All heat transfer plates of HTST, APPS and HHST pasteurizers and all other transfer plate systems in the establishment.

Frequency:

At least once a year and more often if the integrity of the transfer plates is in question.

Criteria:

To check for pinholes in the heat transfer plates.

Apparatus:

Connections and fittings to circulate the back side of all non-product surfaces of plates (i.e. hot water, chill water and glycol sections) and raw side of regenerator in one complete circuit.

Method:

Circulate potassium permanganate solution on both sides of heat exchanger plates. A pinhole in plate will show dye on 2 plates - the one with leak and the one opposite.

Procedure:

  1. Clean up pasteurizer system in a normal manner.
  2. Make necessary connections to circulate the back side of all non-product surfaces of plates (hot water, chill water and glycol sections). This should be accomplished with one circulation to clean all sections at one time.
  3. Fill constant level tank with water. Begin pumping water to flush back side of plates until water runs clear.
  4. Direct flow to constant level tank to start circulation.
  5. Clean both sides of the plates properly with a recommended procedure. Flush thoroughly with warm or hot water.
  6. Open up the heat exchanger. Inspect each plate for proper cleaning. Plates which are not cleaned will need hand scrubbing to get clean.
  7. If plates are clean leave plates spread apart and spaced to allow drying. All plates must be dry and clean before proceeding to the next step.
  8. Close up the heat exchanger. Hook up to circulate non-product side of plates as well as raw side of the regenerator in one complete circuit.
  9. Add water to constant level tank - do not turn on pump.
  10. Mix in potassium permanganate dye in constant level tank using a stirring rod. (Approximately 3.5 kg per 1000 litres water).
  11. Begin pumping potassium permanganate solution and adding water if necessary to keep constant level tank from running dry. Stop adding water when level in constant level tank is satisfied.
  12. Add approximately 4.5 litres liquid caustic solution (or 2.5 kg caustic powder mixed in 5 litres water) to constant level tank.
  13. Heat to 82°C. Turn off the steam supply once this temperature is reached.
  14. Circulate for 30 minutes. Do not be concerned with drop in temperature during remainder circulation period.
  15. Pump dye solution to floor drain until constant level tank runs dry. Do not add water.
  16. Shut off pump when reservoir runs dry.
  17. Disconnect connections. Allow the heat exchanger to drain. Rinse off the floor and outside of the heat exchanger while the heat exchanger is draining.
  18. Open up the heat exchanger and allow to drain completely. Rinse any dye solution traces from exterior of equipment, floor etc.. Inspect each pair of product plates.
  19. A hole in the heat exchanger will show potassium permanganate dye on 2 plates i.e. the one with leak and one opposite.
  20. It will be necessary to manually dye check both plates to determine which is leaking.
  21. After all plates have been inspected reconnect and circulate Oxalic acid at the rate of 100 mL per 45 litres of water through same circuit as the potassium permanganate dye solution to neutralize the dye. Heat to 60°C. Use Oxalic acid solution from the constant level tank to clean dye from all areas where splattering has occurred.
  22. Connect the heat exchanger up for normal product clean-up and re-clean with normal procedure.
  23. Keep records to show proper testing has occurred and corrective action, if required has been taken.

Corrective Action:

Replace all heat transfer plates with pinholes.

Test 20: Pressure Differential Controller

Application:

To those pressure differential controllers having pneumatically driven pointers, used to control the operation of booster pumps on HTST pasteurizers. In the case of product-to-heat transfer medium-to-product type regeneration, the heat transfer medium pump is considered as the booster pump.

Frequency:

Upon installation and at least once every 6 months thereafter.

Criteria:

To verify that the booster pump shall not operate, unless the product pressure in the pasteurized side of regenerator is at least 2 psi (14 Kpa) greater than the product pressure in the raw side of the regenerator.

Apparatus:

Optional - Pneumatic testing device as shown in figure 4.

Method:

The pressure differential controller is checked and adjusted to prevent operation of the booster pump, unless the product pressure in the pasteurized side of the regenerator is at least 2 psi (14 Kpa) greater than pressure in the raw side of the regenerator.

Procedure A:

  1. Loosen the connections at both pressure sensors and wait for any liquid to drain through the loose connections. Observe that both pointers are within ±0.5 psi of zero psi (0 Kpa).
  2. Remove both sensors from the process and mount them in a tee, either at the discharge of the booster pump, or connected to the pneumatic testing device. Note the difference between the sensor readings. The change in elevations of the sensors may have caused some change in the zero readings.
  3. Turn on the booster pump switch and depress the test push button to operate the booster pump. Observe that the difference between the sensor readings is within 1 psi (7 Kpa) of that observed before pressure was applied.
  4. Turn off the booster pump switch and return the pressure sensors to their normal process locations.
  5. Manually move and hold the white pointer (raw side of the regenerator) at the normal operating pressure of the booster pump.
  6. Press the test button while manually moving the orange pointer (pasteurized side of the regenerator) upscale until the pilot light turns on, then slowly move the orange pointer downscale until pilot light turns off.
  7. Observe that the pilot light does not turn on until the orange pointer is at least 2 psi (14 Kpa) higher than white pointer, and the pilot light turns off when the orange pointer is no less than 2 psi (14 Kpa) higher than the white pointer.
  8. If necessary, adjust the differential setting.

Note: The test may also be completed using a pneumatic testing device capable of producing differential pressures on the probes. This device should be capable of performing and be operated in a manner so as to duplicate the conditions described above.

Procedure B:

Application:

As above and to electronically operated pressure differential controllers.

Procedure:

  1. Follow steps 1) and 2) in procedure A.
  2. Operate the system in forward flow.
  3. Reduce the pressure in the pasteurized product regenerator section by slowly opening the back pressure control valve, or increase the raw product pressure by slowly opening the flow control valve (if present) located between the booster pump and the raw product pressure sensor.
  4. Observe that the booster pump stops and the pressure differential controller pilot light goes out when the pasteurized product pressure is no less than 2 psi (14 Kpa) higher than raw product pressure. The booster pump cut out point is indicated by sudden decrease in raw product pressure.

Note: The 2 psi (14 Kpa) differential represents the sum of the 1 psi (7 Kpa) differential required between raw and pasteurized product in the regenerator, plus the 1 psi (7 Kpa) imprecision permitted between the two pressure sensors. Should the pasteurized milk regenerator outlet be at the bottom of the pasteurizer, the pressure differential must be increased by the head pressure within the pasteurizer.

Note: This test may also be completed by using a pneumatic testing device consisting of two independently adjusted pressure connections to simulate raw and pasteurized product pressure conditions.

Figure 4 - Pneumatic Testing Device
Figure - Pneumatic Testing Device. Description follows.
Description of image - Pneumatic Testing Device

This schematic describes the basic design and components of a pneumatic testing device. Components are:

  • Air gauge or sensing element
  • Reducer
  • Tee
  • Pressure switch or sensing element
  • Reducer
  • Cap of correct type, drilled and tapped to accept ¼" pipe
  • 0-100 PSIG gauge ½% accuracy
  • Needle valve
  • Vent
  • Pressure regulator
  • Air supply min. - 70 PSIG (pounds per square inch gauge)

Test 20.1: Interwiring of the Pressure Differential Recorder Controller with the Flow Diversion Device

Application:

  1. To all differential pressure controllers used to control the operation of flow diversion devices on HHST systems when no vacuum breaker is located downstream from the holding tube, and
  2. To all differential pressure controllers used to control the operation of flow diversion devices, product divert systems, product divert valve(s) or other acceptable control systems used in APPS.

Frequency:

Upon installation and at least once every 6 months thereafter.

Criteria:

The differential controller shall be interwired with the flow diversion device so that divert occurs when the sterilized product pressure in the regenerator drops to less than 2 psi (14 Kpa) from that on the raw side of the regenerator and remains in diverted flow until proper pressures are re-established. In the case of product-to-heat transfer medium-to-product regenerators, where the protection is on the pasteurized or aseptic side, the "heat transfer medium" side of the regenerator is considered to be the "raw product" side for purposes of this test.

Apparatus:

  1. Sanitary pressure gauge.
  2. Pneumatic testing device as shown in Figure 4.

Method:

The differential pressure switch is checked and adjusted to prevent forward flow, unless the product pressure in the pasteurized side of the regenerator is at least 2 psi (14 Kpa) greater than the pressure in the raw product side of the regenerator. In the case of product to water to product regenerators protected on the pasteurized or aseptic side, the water side of the regenerator shall be considered to be the "raw product" for purposes of this test.

Procedure:

  1. Wire the test lamp in series with the signal from the pressure differential switch to the flow diversion device.
  2. Calibrate the pressure switch and probes (using Test 20, Procedure A).
  3. Adjust the pressure on the pressure switch sensors to their normal operating pressures (with the pasteurized, or aseptic pressure at least 14 Kpa (2 psi) higher than the raw product pressure.
  4. The test lamp should be lit. If the test light is not lit, increase the pasteurized, or aseptic pressure (or lower the raw product pressure) until the test light is lit.
  5. Gradually lower the pasteurized, or aseptic side (or raise the raw product pressure) until the test light turns off.
  6. The test light should turn off when the pasteurized or aseptic pressure is at least 14 Kpa (2 psi) higher than the raw product pressure.
  7. Note the differential pressure at the point the light turns off.
  8. Gradually raise the pasteurized, or aseptic pressure (or lower the raw product pressure) until the test light turns on.
  9. The test light should not turn on until the pasteurized, or aseptic pressure is greater than 14 Kpa (2 psi) higher than the raw product pressure. Note the differential pressure at the point the light turns off.
    Note: This test may be completed using a pneumatic testing device capable of producing differential pressures on the probes. This device should be capable of being operated in a manner so as to duplicate the conditions described above.
  10. Seal the instrument and record the test results for the office record.

Test 21: Pressure Gauges - Displays

Application:

Pressure display of the pressure differential controller and to all pressure gauges on the HTST pasteurizer and any other heat transfer plate systems to monitor pressure.

Frequency:

Upon installation and at least once every 6 months thereafter, and whenever the gauges are adjusted or repaired.

Criteria:

Required pressure gauges and displays shall be accurate.

Apparatus:

  1. Pneumatic testing device as shown in figure 4 or equivalent.
  2. Pressure gauge of known accuracy.

Method:

Verify the accuracy of required pressure gauges and displays with an accurate gauge.

Procedure:

  1. Pressure gauge of known accuracy is connected to one outlet of test apparatus.
  2. Pressure gauge or display sensor being checked is connected to the second outlet of the sanitary tee.
  3. Air is bled into system through third outlet and comparative readings are made throughout the normal operating range for that gauge or display.
  4. Record results.

Corrective Action:

Inaccurate gauges or displays should be returned to the factory for repair. It is not recommended that the plant operator attempt the adjustment of pressure gauges.

Test 22: Booster Pumps - Interwired with Flow Diversion Device

Application:

To all booster pumps used for HTST pasteurizer systems. In product-to-heat transfer medium-to-product type regeneration, the heat transfer medium pump is considered as the booster pump.

Frequency:

Upon installation and at least once every 6 months thereafter, and after any change in the booster pump or switch circuits.

Criteria:

The booster pump shall be wired so it cannot operate if the Flow Diversion Device is in the diverted position.

Apparatus:

  1. Pneumatic testing device as shown in figure 4.
  2. Sanitary pressure gauge.
  3. Suitable means of heating the water bath.

Method:

Determine if the booster pump stops by dropping the temperature and causing the Flow Diversion Device to divert.

Procedure:

  1. Connect pasteurization pressure sensor to the tee of the testing device with the other end of the tee capped.
  2. Turn on the air supply to provide an adequate pressure differential.
  3. Place the Safety Thermal Limit Recorder probe in the hot water bath, which is above the cut-in temperature.
  4. Cap the Safety Thermal Limit Recorder probe and pasteurized sensor port if the pasteurizer has water in it.
  5. Turn on the Flow Control Device. At this time, the booster pump should start to run.
  6. Remove the Safety Thermal Limit Recorder probe from the hot water bath.
  7. When the Flow Diversion Device moves to the diverted flow position, the booster pump must stop.
  8. Ensure that the pressure differential remains adequate and the Flow Control Device continues to operate following its momentary pause during the Flow Diversion Device transition.
  9. Record the test results.

Corrective Action:

If the booster pump fails to stop when the flow-diversion device is in the diverted flow position, have the plant maintenance personnel check the wiring and correct the cause.

Test 23: Booster Pumps - Interwired with Pressure Differential Controller

Application:

To all booster pumps used for HTST pasteurizer systems. In product-to-heat transfer medium-to-product type regeneration, the heat transfer medium pump is considered as the booster pump.

Frequency:

Upon installation and at least once every 6 months thereafter, and after any change in the booster pump or switch circuits.

Criteria:

The booster pump shall be wired so it cannot operate if the pasteurized product pressure in the regenerator does not exceed, by at least 2 psi (14 Kpa), the product pressure in the raw side of the regenerator.

Apparatus:

  1. Pneumatic testing device as shown in figure 4.
  2. Sanitary pressure gauge.
  3. Suitable means of heating the water bath.

Method:

Determine if the booster pump stops when the pressure differential is not properly maintained in the regenerator.

Procedure:

  1. Connect pasteurization pressure sensor to the tee of the testing device with the other end of the tee capped.
  2. Turn on the air supply to provide an adequate pressure differential.
  3. Place the Safety Thermal Limit Recorder probe in the hot water bath, which is above the cut-in temperature.
  4. Cap the Safety Thermal Limit Recorder probe and pasteurized sensor port.
  5. Turn on the Flow Control Device. At this time, the booster pump should start to run.
  6. Decrease the air supply to the testing tee until the pressure is less than 2 psi (14 Kpa) of the pressure on the raw milk pressure sensor. The booster pump must stop.
  7. Ensure that the Flow Diversion Device remains in the forward flow position and the Flow Control Device continues to operate.
  8. Record the test results.

Corrective Action:

If the booster pump fails to stop when the pressure differential is not maintained, have the plant maintenance personnel determine and correct the cause.

Test 24: Booster Pumps - Interwired with Flow Control Device (Timing Pump, Metering Pump)

Application:

To all booster pumps used for HTST (In product-to-heat transfer medium-to-product type regeneration, the heat transfer medium pump is considered as the booster pump). To all feed and heat transfer medium pumps used in HHST and aseptic processing systems.

Frequency:

Upon installation and at least once every 6 months thereafter and after any change in the pumps or switch circuits.

Criteria:

The booster/heat transfer medium/feed pump shall be wired so they cannot operate if the Flow Control Device is not in operation.

Apparatus:

  1. Pneumatic testing device as shown in Figure 4.
  2. Sanitary pressure gauge.
  3. Suitable means of heating the water bath.

Method:

Determine if the booster/heat transfer medium/feed pump stops when the Flow Control Device is off.

Procedure:

  1. Connect pasteurization pressure sensor to the tee of the testing device with the other end of the tee capped.
  2. Turn on the air supply to provide an adequate pressure differential.
  3. Place the Safety Thermal Limit Recorder probe in the hot water bath, which is above the cut-in temperature.
  4. Cap the Safety Thermal Limit Recorder probe and pasteurized sensor port.
  5. Turn on the Flow Control Device. At this time, the booster/heat transfer medium/feed pump should start to run.
  6. Turn off the Flow Control Device. The booster/heat transfer medium /feed pump must stop.
  7. Ensure that the pressure differential remains adequate and the Flow Diversion Device remains in forward flow position. Record the test results.

Corrective Action:

If the booster/heat transfer medium/feed pump fails to stop when the Flow Control Device has been turned off, have the plant maintenance personnel determine and correct the cause.

Date modified: