Dairy Engineering

Module 4. Homogenizers

Lesson 15
CARE AND MAINTENANCE OF HOMOGENIZERS, ASEPTIC HOMOGENIZERS

15.1 Introduction

Homogenizer is heavy equipment, operating at high pressures. Hence, the care and maintenance is important for the long useful life of machine, and safe operation of this high pressure machine.

The condition of Homogenizer can be known from the extent of breaking of fat globules after homogenizing. The Homogenizing efficiency is found by either direct microscopic method or by cream layer method.

15.2 Valves

The homogenizer valves over a period of use, will lose its proper shape, and may form grooves. It needs to be reground or replaced. If the seals of the valves are leaking, they have to be replaced immediately. The faces of the valve and valve seat must be kept in good serviceable condition to retain an efficient homogenization of the product. This can be recognized by the amount of wear that initiates at the bore of the valve and radiates out across the face. If the wear is up to two-thirds of the surface area, relapping of the valve with carborundum paste between faces can rectify this but further wear will allow erosion grooves to appear, recognized by straight lines radiating outward, and loss of homogenization will rapidly occur.

Fig. 15.1 Homogenizer valve wear

15.3 Pressure Gauges

The pressure gauges measuring the pressure of milk must have stainless steel components and should be filled with glycol fluid to reduce corrosion and damping the vibrations. The gauges must be calibrated from time to time. The pressure gauges measuring the oil gauges must also be check for calibration frequently.

15.3.1 Safety valve

It has to be tested for its setting, and whether it releases pressure at the set point, by use of Hydraulic test pump.

15.3.2 Reducing pressure fluctuations

Reducing pressure fluctuations in suction side and discharge side is very important in effective operation of Homogenizer, as well as its effect on the related equipment like Pasteurizer to which it is connected. For this, generally, the Air cylinders are fixed both on suction and discharge pipelines connected to Homogenizer. The Air cylinders have air in the vessel that is cylindrical and in an inverted position, connected to the pipeline. As the pressure increases in the pipe line, the air in the cylinder gets compressed, resulting in a slight reduction in the line pressure. In the next stage in the cycle of operation, during suction stroke, the pressure in the line decreases, during which, the air in the vessel, which is at higher pressure related to the line pressure, will now expand, replacing some of the fluid that has entered into the vessel. Thus, the pressure fluctuations in the pipeline are reduced to some extent.

15.4 Power Drive

1. Whenever drive motor is repaired / replaced, the direction of rotation has to be checked, as the same shaft is most probably driving the lubrication mechanism, and would not deliver the lubrication oil at the required pressure, even if the rotation is slow.

2. The bearings, belts are to be replaced when necessary as per the preventive maintenance schedule. The lubrication oil, or the cooling water should not be spilling where belt drive is located, as it would cause slippage and damage to the belt.

3. Replacing V-belts one at a time (when wear is detected on one only) is a risky operation since the new one - being shorter - is likely to carry most of the load. Belts must be tensioned correctly to transfer the drive and prevent unnecessary wear. The following are suggestions on how to do a simplified testing during routine maintenance inspection. When stopped, a correctly tensioned V-belt should, if pressed firmly with the thumb near the mid-point (half way from centre to centre), depress 3/4 of its own thickness for each one metre centre to centre distance.

During assembling and disassembling, the dismantled parts must be kept on table over a rubber mat to prevent damage to the parts as well as to avoid any contamination.

A daily inspection should be made of the oil level visible through the sight glass at the rear of the machine. Lubrication oil should be replaced regularly, as per manufacturer’s instructions, and its pressure to be maintained while running the equipment. After draining off any condensate from the oil sump through the pet cock, oil should be added if required, before starting up the homogenizer. The oil should be completely drained and replaced, after every 6 months.

The levelling of homogenizer should also be maintained, as it is likely to get disturbed over the period due to vibrations during operation.

Cooling water should of the quality and flow rate recommended by the manufacturer. The flow to the piston rods should be sufficient, especially if water is cooling the oil.