FAO ANIMAL PRODUCTION AND HEALTH PAPER 45
Maintenance systems for the dairy plant
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FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 1984
In most developing countries dairy equipment is imported, spare parts procurement is troublesome and specialized dairy machinery servicing from outside the milk plant is either scarce or non-existent. Under such conditions the successful operation of the milk plant depends largely on the performance of the engineering staff employed. This publication attempts to provide the dairy engineers in milk plants in developing countries with information and guidelines on methods used and means required to successfully accomplish their difficult tasks.
Special acknowledgement is given to the following who have provided information and illustration material for this publication:
APV International Limited, Crawley, Surrey, U.K.
Dairy Trade Federation, London, U.K.
Milk Marketing Board, Thames Ditton, Surrey, U.K.
Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics.
|CHAPTER I.||PREVENTIVE MAINTENANCE|
|A.||Inspection based on log book entries|
|B.||Scheduled inspection combined with schedule servicing|
|C.||Scheduled inspection of non–standard items|
|D.||Inspection schedules recording|
|4.||Spare parts programme|
|6.||Maintenance workshops and equipment|
|CHAPTER II.||TRAINING OF DAIRY INDUSTRY ENGINEERS|
|1.||Training Needs Analysis (TNA)|
|CHAPTER III.||MAINTENANCE OF SERVICE EQUIPMENT|
|2.||Centrifugal pumps, fans, air compressors|
|3.||Ventilating and exhaust fans|
|10.||Steam raising equipment|
|CHAPTER IV.||MAINTENANCE OF PROCESS EQUIPMENT|
|1.||Pumps and piping|
|B.||Swept surface heat exchangers|
|C.||Tubular heat exchangers|
|4.||Milk storage and process tanks|
|5.||Agitators and mixers|
|A.||Temperature controllers and recorders|
|8.||Evaporators and spray driers|
|9.||In-place cleaning equipment|
|CHAPTER V.||MAINTENANCE OPERATIONS|
|1.||Safety at work|
|2.||Hygienic working practices|
|4.||Examples of routine maintenance procedures|
|Figure1||Equipment record card (example)|
|2||Flow diagram of pasteurization plant as log book recording guide (example)|
|3||Example of log book page with recorded entries|
|4||Maintenance inspection schedule card (example)|
|5||Creamery engineering management structure|
|6||Example of training analysis - Sheet A|
|7||Example of training analysis - Sheet B|
|8||Training needs analysis|
|9||Piston packings and rings - dismantling and assembly|
|10||Wear pattern - homogenizing or pressure control valve or seat|
|11||General arrangement of pressure lubrication system for homogenizer drive gears and bearings|
|13A||Hazard warning signs in U.K.|
|13B||Hazard warning signs and safety colours in U.K.|
|14||Six-step approach to diagnosis of faults|
|15||Guide to fault-finding in the system|
|16||Half-split approach to fault diagnosis|
|17||Types of screwheads|
|18||Types of nuts|
|19||Types of washers|
|20||Shims used as packing|
|21A||Types of bearings|
|21B||Types of bearings|
|23B||Bearing removal screws|
As soon as a milk plant is established and commissioned the need for an effective system of maintenance begins in order to maintain output at the desired level. Such a system must be planned in detail in advance and the need must be foreseen in the original planning of the plant.
The spacing of equipment items must be adequate for replacement of components as well as for operation. The building must be designed so that any item of equipment can be removed at some future date. Experience may reveal that these objectives have not been met: if so modifications to the layout of equipment or to the building should be made at the earliest opportunity before a breakdown makes the work necessary so increasing the problem of repair, and delaying operations to restore normal output. The principles of preventive maintenance are discussed in detail in Chapter One.
The primary objective of a planned maintenance system is to prevent breakdowns. While every failure cannot be anticipated, regular inspection and servicing are the best means of preventing failure during operation of the equipment. Renewable components such as joint rings or rubber seals are replaced routinely according to a predetermined schedule. The necessary supply of spare parts is thus known in advance, and this simplifies the procedure of stores control.
However comprehensive the system of preventive maintenance, occasional breakdowns inevitably occur. They may be due to faulty components, incorrect assembly, failure to observe correct operating procedures or some other unforeseen cause. When such a break-down occurs the product line must be stopped with consequent loss of output. In some cases duplicate equipment is already installed, for example clarifiers and cream separators are often duplicated to facilitate interim cleaning. Packaging is often divided into several parallel lines so that failure of one line merely reduces output. Heat exchangers are usually not duplicated so that breakdown inevitably brings most processes to a stand-still.
The maintenance section must therefore include immediate repair facilities covering a wider range of skills and resources than otherwise would be necessary for routine preventive maintenance. The needs are discussed more fully in Chapters 1 and 2. Breakdowns inevitably mean loss of product and therefore income. Substantial wastage may result, and if the breakdown cannot be rectified within a few hours the following day's operations are jeopardized. Diversion of the incoming milk to another plant may become a necessity, with all the complications and possibly wastage, that this entails.
Milk and most milk products are highly perishable because they are excellent nutritive media for micro-organisms, which inevitably gain access and cause spoilage through souring. It is virtually impossible to prevent contamination in the process of milking and handling, but spoilage can be delayed by cooling at the farm or at reception in the milk plant to 4°C within two or three hours of milking. This requires refrigeration, and therefore effective maintenance of the refrigeration equipment becomes a vital factor at an early stage. Cooling delays the growth of most micro-organisms for one or two days, after which heat treatment to kill most of the organisms present becomes necessary to extend the life of the milk for liquid consumption or for processing into milk products. This treatment is known as ‘pasteurization’. Hence maintenance of the heat treatment equipment and the steam supply is essential to ensure product quality.
In the case of milk for liquid consumption and most fresh milk products such as cream, yoghurt and soft cheese, further cooling to 4°C is essential after processing and they must be maintained at this temperature after packaging until the point of sale. Effective maintenance of the refrigeration equipment is again essential to ensure a high product quality. Only in the case of milk for liquid consumption (treated by the ultra-high temperature (UHT) process and packaged aseptically), ghee and milk powder, is subsequent re-frigeration unnecessary. Butter must be stored at low temperature - at 0-4°C for short-term or at up to 22°C for long-term storage. Hard cheese requires a storage temperature of about 10°C, necessitating refrigeration in most climates.
The continuous supply of steam for heat treatment during process operations and of constant refrigeration are so vital to the operation of the milk plant that at least one steam boiler and one refrigeration compressor are normally installed surplus to maximum operational requirements. This provides the opportunity for routine cleaning and maintenance and periodical inspections which may be required by law or for insurance purposes, and which require more time than is available between daily operations. In the case of unforeseen breakdowns, this space capacity minimizes the delay in restarting process operations.
Cooling delays the growth of micro-organisms which gain access to the milk up to the time of pasteurization. This heat treatment kills all pathogenic organisms and a high proportion of others but there are some which can form spores and survive the treatment. These can subsequently grow to cause spoilage. Thus there is good reason at every stage from milking to packaging to minimize contamination. Most contamination comes from equipment surfaces as a result of inadequate cleaning after previous use. This is the responsibility of the processing staff and may be caused by bad design. If so it should be reported and rectified. Nevertheless a guiding principle in all maintenance operations involving milk contact surfaces should be to work in the most hygienic conditions possible.