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Expert Advise 
From People Who Understand The Food Industry

C.I.P sets their make up and maintenance

N Moralee 1999

This document is designed as a general guide to the items found on C.I.P sets, what they do and when to maintain them.




1. Typical components found on CIP sets

2. Why carry out maintenance ?

3. What is Total Productive Maintenance.

4. Calibration and general checks

5. Schedule of maintenance.


Old CIP Set Does your CIP set look this bad ?

Ever wondered why it's not reliable?


Section 1

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This list details the items commonly found on CIP sets and gives a brief explanation of what they are for and how they operate. This section is intended to give a general insight into the items and is not intended as a detailed explanation.

· CIP tanks

The basic body of a CIP set can vary in size depending on the design and duty of the set, but should hold enough liquid to completely fill the largest cleaning circuit plus 25% reserve. The usual lay out for a CIP set is to have three tanks to contain:- fresh water, detergent and reclaimed water. A fourth tank may be found on some systems to hold a second detergent. The tanks may be round, square or rectangular as dictated by the location of the set, however round with a conical bottom is the best in terms of cleaning and de-sludging. The material of construction will be dictated by the type of detergent being used but Stainless Steel to ASI316 is the best for food industry use.

· Heating coils

This is a bent tube fitted inside some CIP tanks and is designed to carry a heating medium (usually steam). Heating coils are notorious for causing problems in CIP sets as they are prone to scaling, corrosion, physical damage. If at all possible avoid heating coils. Where there is no alternative to the heating coil a regular routine maintenance scheme should be set up. A detergent monitoring system should be fitted to the heating medium return lines to give early warnings of leaking coils.

· Level Probes

The level probe is designed to indicate a particular level within a tank. Level probes in CIP sets are usually set to indicate :- high level, low level & working level. On occasions additional probes may be used to indicate emergency high & emergency low levels. In general there are two operating principals used for level probes

1. Conductivity, an electrical current is passed along the probe to the liquid and from the liquid to the tank wall or to a second probe, when the liquid is below the level probe the electrical circuit is broken and the electrical current can not flow.

2. Capacitance, these types of probe work because the capacitance of a material will vary as it becomes immersed in a liquid. Capacitance probes offer the advantage that they can be used in liquids that do not conduct electricity and only a single probe is needed. The disadvantage is that they cost considerably more than conductivity based level probes and require more complex maintenance.

3. Float type level switches, these operate by a float moving as the liquid rises and falls. A mechanical switch is activated by the float. Care should be taken selecting float type switches as some types can be fouled by the build up of detergent chemicals. The largest practical float should be chosen to give the greatest buoyancy and to have sufficient weight to damp out the effects of splashing and turbulence in the tank. Floats in a tube external to the tank are a better proposition offering easier maintenance. Some types offer level indication by using revolving magnetic sections that change colour as the float carries a magnet past them.

· Valves

There are numerous designs on vales fitted to CIP sets but the most common is the Automated "Butterfly" valve. This type of valve has a disc that pivots along the centre line that allows or prevents flow. The "Butterfly" valve is designed to be either open or closed and as a consequence does not work well when used to throttle the flow of a liquid. "Butterfly valves are relatively cheap and relatively easy to maintain as there is only one moving part (the butterfly disc) and only one rubber seal to wear. Routing valves of various designs will also be found on CIP sets. These are easily distinguished as they have at least three ports, allowing the liquid to be routed from the inlet port to any of the outlet ports. Routing valves because of their increased complexity are more costly to install and maintain than "butterfly" valves, however in situations where numerous CIP routes are required the routing valve comes into its own, often replacing several "butterfly" valves.

· Sight glasses

The sight glass is a length of transparent tube fitted to the side of a tank and running vertically from top to bottom. The sight glass allows the level of liquid in the tank to be visually assessed. As sight glasses are difficult to keep clean and when made from plastic tend to discolour and distort they are losing favour in the food industry generally and are being replaced with level gauges.

· CIP pumps

CIP pumps fall into roughly three groups:-

1. Delivery pumps, usually centrifugal offering high flow relatively low pressures (up to 4 Bar) and are designed to work best with a flooded suction. These are used to deliver the cleaning solutions to the item of plant being cleaned. Centrifugal pumps are relatively easy to maintain and are fairly inexpensive to purchase.

2. Mixing pumps, usually of the same design as delivery pumps but of smaller capacity. These are usually fitted to ensure adequate mixing of the detergents.

3. Scavenge or return pumps, these pumps return cleaning solutions from items of plant (usually tanks) that are being cleaned to the CIP set. They should be designed to pump well even without a flooded suction, this allows them to cope with the large quantities of air that become entrained in the cleaning solutions during CIP. Liquid ring type pumps are generally more successful than centrifugal pumps for this duty. Liquid ring pumps are relatively easy to maintain but are significantly more expensive to purchase than a centrifugal pump.

· Conductivity probes

These probes are designed to measure the electrical conductivity of a solution, consequently they can be used to measure the strength of ionic detergents (acid or caustic based detergents). These probes are generally reliable needing little maintenance but regular calibration. [These probes should not be confused with level probes that use the conductive properties of a liquid ].

· Flow switches

These come in three main varieties:

1. Flap type flow switch. A small flap fits into the pipework and is deflected by the flow of liquid, this deflection physically activates a switch. This design is of little use in CIP systems as debris often collects around the flap and prevents proper operation.

2. Thermistor switched flow sensors. A thermistor is fitted into the wall of the pipework and as a liquid flows past the unit heat is removed from the thermistor, this removal of heat alters the thermistor's ability to carry an electrical current. The alteration in electrical current can be detected and used to determine if there is liquid flowing in the pipework. In CIP systems where the temperature of the liquids can vary considerably thermistor flow sensors are unreliable, consequently they are not seen to any great extent these days.

3. Tuning fork detectors. These units use a type of tuning fork inserted into the pipework to check for liquid flow. One leg of the fork vibrates at a known frequency and the other leg of the fork receives the vibrations transmitted through the liquid. Due to the Doppler effect the transmitted frequency will be altered by the flow of the liquid, so by comparing the received frequency with the transmitted frequency not only can the flow be detected but its direction can be established. This type of probe is becoming increasingly popular as they are reliable and incur little maintenance cost.

· Flow meters

There are numerous designs of flow meter, however only a few are suitable for CIP systems. A CIP flow meter must be able to cope with the following: A wide range of temperatures, Caustic and Acid cleaning materials, Large quantities of entrained air, Solid debris in the liquid being measured, With this in mind only two types of meter are in common use:

1 The electromagnetic flow meter, these units work by measuring the disturbance in a magnetic field caused by the passage of a conductive liquid. As the disturbance is proportional to the flow then the flow can be indicated.

2 The tuning fork type using the Doppler principle. These units are very similar in design to the flow switches based on this principle, but with extra electronics to calculate the flow of the liquid from the measured deviation in the received frequency. As these units are considerably cheaper to purchase than the electromagnetic flow meter they are rapidly gaining popularity. As the Doppler principle does not rely on conductivity these units can measure flow in non conductive liquids, oils being a typical non conducting liquid.

· Temperature probes

Temperature probes fall broadly into two groups:

1 Probes that rely on the expansion of a material as temperature increases, in this group you will find Mercury in glass thermometers and Borden tube gauges. These types of temperature probes generally can only give an indication of temperature close to the item being measured (typically 1- 2 metres). As glass is unacceptable in a food production environment; a glass based thermometer should not be found on a CIP system.

2 Electrical temperature probes. These probes generally work because the electrical conductivity of certain materials varies with temperature consequently the temperature can be calculated. There are some materials that have a specific and predictable electrical resistance at a given temperature, these types of material are used to produce "resistance thermometers". Resistance thermometers are now far more common than the older thermistor probes, this is because resistance thermometers have a known resistance at a given temperature so probes can generally be swapped or changed without the need for re-calibration. Thermistor based systems will need a greater input in terms of calibration and maintenance so are starting to disappear in industries that do not have a specific need for them.

· Chart recorders

The chart recorder can be found in a multitude of different guises, from simple single pen circular charts to complex multi-pen fan-fold systems. In general all chart recorders need the same sort of simple maintenance: Calibration, Replacement of the ink or printing system

· Chart recorder Controllers

These units are basically chart recorders with additional electronics to enable them to have some control over the parameters being measured. Maintenance will be as for simple chart recorders with the added maintenance needed for the control electronics and any associated control equipment.

· Level sensors

These are frequently found on CIP set detergent tanks instead of level probes. The measuring techniques are varied and numerous so I will deal with the most common types.

Infra red sensors, these operate by transmitting a beam of infra red light towards the surface of a liquid and measuring the time required for the reflected light to reach a sensor, the further the liquid is from the sensor the longer the light takes to reach it. Once a tank has been calibrated then it contents can be calculated for any sensor to liquid distance. Infra red has the disadvantage that it is easily confused by steam or water vapor in the air between the liquid and the sensor and by condensation on the sensor itself; as these conditions are common in CIP sets it makes infra red sensing unreliable for this type of duty.

Ultrasonic sensors, these operate by transmitting a beam of Ultra sonic sound towards the surface of a liquid and measuring the time required for the reflected light to reach a sensor, the further the liquid is from the sensor the longer the light takes to reach it. Once a tank has been calibrated then it contents can be calculated for any sensor to liquid distance. Ultra sonic has the disadvantage that it is easily confused by foam and froth on the liquid and by condensation on the sensor itself; as these conditions are common in CIP sets it makes Ultra sonic sensing unreliable for this type of duty.

Radar based sensors, these operate by transmitting a beam of Radar waves towards the surface of a liquid and measuring the time required for the reflected beam to reach a sensor, the further the liquid is from the sensor the longer the light takes to reach it. Once a tank has been calibrated then it's contents can be calculated for any sensor to liquid distance. As radar is unaffected by moisture, steam or froth it is particularly good for CIP systems and this sort of device is becoming more common as the price falls to levels comparable with other systems.

Pressure transducer systems, these devices are relatively cheap to install. Operation is by measuring the pressure exerted by the liquid in a tank and generating an electrical or pneumatic signal that can be displayed and used to pass information to the CIP control system. When installing this type of device a valve should be fitted between the tank and the pressure sensor, so that maintenance can be carried out without draining the tank.

· Turbidity monitors

Turbidity monitors, these devices give an indication of how much product is in a solution passing the sensor. They operate by measuring the amount of light the liquid absorbs from a known light source. To achieve this a light transmitter and receiver are fitted into a pipeline and the liquid to be measured passes between them. It must be noted that other non product substances such as air bubbles or detergent can also absorb light, so the use of turbidity sensors needs to be controlled carefully.

Section 2

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Why carry out maintenance ?

If maintenance is not carried out a never ending cycle forms:

This cycle is vicious and difficult to break out of.

This cycle is common with CIP sets, as in general they are installed in areas of the factory that are "tucked out of sight", leading to an attitude that the CIP set is not part of the general production equipment.

If this cycle has formed than the production site will experience "break downs" that are both costly and time consuming. The very nature of a "break down" is that the CIP set will fail to operate correctly when it is needed. The subsequent repairs will be rushed, by staff that should be performing other tasks and doubtless at premium payment rates. Maintenance on the other hand can be performed at a time convenient to the production process, when suitable skills and labour are available at normal costs.

The worst and most insidious form of CIP set "break down" is one that does not disable the sets operation but simply prevents a critical parameter from being achieved. This type of fault is worst on a CIP set that does not monitor its own performance sufficiently. An example of this sort would be a temperature probe failing. Imagine the following situation :

The temperature probe has failed (and not been detected by operational staff),

A clean fails to reach the required temperature to sanitise the process plant,

The next production run produces product that is contaminated (bacteriological samples are taken, 72 hours incubation),

The next production run produces product that is contaminated (bacteriological samples are taken, 72 hours incubation),

The next production run produces product that is contaminated (bacteriological samples are taken, 72 hours incubation),

The first set of bacteriological results are obtained (product is held or withdrawn),

An investigation is started and production stopped. (the investigation may take some time to find the fault),

The second days product is held or withdrawn,

The third days product is held or withdrawn.

The fault is identified and the probe repaired. The process plant can be re-cleaned and production re-started.

Due to the failure of a temperature probe costing a few pounds, three days production can be lost.

This scenario is designed to show how the lack of maintenance on a CIP set can affect the output of a production unit.

How do you break out of this cycle ?

Section 3

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Total Productive Maintenance (T.P.M)

T.P.M will lead to continuous improvements in the performance of any plant it is applied to

. The performance of the equipment needs to be measured and reviewed on a regular basis.

One way of doing this is to monitor the Quality Rate (Q.R).

Calculating the "Quality Rate", this lets you know how much was produced at the right quality first time.

There is no worse form of waste than having to "re-work" or dump product that was manufactured incorrectly.

The calculation is as follows:

(Output - quality failures x 100) / Output = Quality Rate %

Records of the Q.R should be reviewed regularly and used to identify problems with the system that need to be prioritised and eliminated

Along with the Quality Rate the "Overall Equipment Efficiency" should be calculated and reviewed.

The "Overall Equipment Efficiency" (O.E.E) can be calculated as follows:

Plant availability x Actual Output x Quality Rate / Maximum Output = O.E.E

This figure gives you a good overview of how the plant and process are performing.

It takes into account almost all of the factors that can affect the overall output of the equipment and compares with it with the potential output.

As each problem with the plant is identified and passed to the problem solving section the aim should be to eliminate this item as a problem completely and not just "how do we get things running again today ?".

Section 4

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Calibration checks

The calibration of instrumentation is every bit as important as the maintenance, "an incorrect reading is worse than no reading"

On CIP sets the following items will need calibration:


Plant Instrumentation Recommended Calibration Interval
Flow (switches) Monthly
Flow (meters) Annually
Conductivity (detergent strength) Weekly
Chart recorders & recorder controllers 6 months
Temperature Probes (thermistor) 3 months
Temperature Probes (resistance) 6 months
Temperature Thermometer 6 months
Turbidity Monitors Annually
Level (gauges) 6 months
Level (probes) Annually
Level (sensors) 6 months

Section 5

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Maintenance schedules

This schedule is designed to offer general guidelines to start CIP set maintenance, but should be modified continually in light of experience with particular plants.

The periods between maintenance should be as long as is possible without risking a breakdown. There is no point replacing a component every year if its operational life is proven to be 36 months, in this case I would set the replacement dates at 33 months. This will allow 3 months grace in which to organise and complete the items replacement.


...Plant Item... ...Maintenance Interval...
Valve rubbers Inspection 6 Monthly
Valve rubber replacement 18 Monthly
Pneumatic valve actuators Annually
Electrical solenoid valve actuators 6 Monthly
Inline filters (filter mesh and joints) Annually
Pump seals ( casing) Annually
Pump seals (shaft) Annually
Pump Impeller check 6 Monthly
Air line water traps (check and empty) 3 Monthly
Level probes Inspect electrical connections Annually
Level sensors Inspect electrical connections Annually
Emergency stop system 3 Monthly
Level floats (leaks) Annually
Level floats (general operation) 6 Monthly
Chart recorders Annually
Recorder controllers Annually
Indicator lights (bulb replacement) Annually
Safety switches (electrical and mechanical operation) Annually
Pipe line joints (replacement) 18 Monthly
Sight glasses 6 Monthly
Tanks (general fabric and lagging) Annually
Steam Coils 6 Monthly
Plate Heat exchangers Annually
Tubular Heaters Annually

This list is meant as a guide only.

Contact points

Tel. 01823 680119 

Mobiles. 07768 981196 

Fax. 01823 680119 

E-mail nem@nem.org.uk

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1999 - N.E.M Business Solutions UK. 
Tel / Fax 01823 680119 or mobile 07768 981196