Lubrication Points on a Vacuum Pump: Which Part Needs Lubrication, and When

Table of Contents

• Why Lubrication Matters
• The Main Lubrication Points on a Vacuum Pump
• Bearing Lubrication: Too Little or Too Much?
• Oil Checks on Oil-Sealed Pumps
• Signs of Incorrect Lubrication
• Tracking and Recording Lubrication

The internal parts of a vacuum pump work by rubbing against each other. What keeps this friction under control is lubrication. Lubrication points vary with pump type and design, but knowing which point needs lubricating, when, and with which material greatly reduces bearing failures and early wear. This article explains the lubrication points and how to track them in a simple way.

Why Lubrication Matters

Lubrication limits wear and heating by placing a thin film between rubbing surfaces. Insufficient lubrication leads to early fatigue of rolling bearings and shaft bearings. High friction also increases motor current and raises the temperature of the pump.

Lubrication problems usually develop slowly. A change in sound, slight heating or a gradual rise in motor current can be among the first signs.

Lubrication is the most basic maintenance operation for a vacuum pump, preventing wear by placing a protective film between rubbing surfaces. Bearings, shafts, couplings and gears are damaged within a very short time without lubrication. Correct lubrication is the precondition for the pump to work quietly, efficiently and for a long life.

Another function of lubrication is to reduce the heat produced by friction. The oil takes heat from the rubbing surfaces and carries it to the outer surface of the pump or to the cooling system. When lubrication is insufficient, both friction and heat increase, and this cycle can quickly turn into a breakdown.

Lubrication also reduces noise and limits vibration. The oil film prevents metal parts from striking each other directly and so lowers the sound. For this reason a change in the sound of the pump is often the first sign that lubrication has become insufficient.

The importance of lubrication varies with the type of pump. In oil lubricated pumps the oil performs both lubrication and sealing, whereas in dry type pumps lubrication is limited to certain points. It should be remembered that the lubrication points and the type of oil differ for each type.

The Main Lubrication Points on a Vacuum Pump

On a vacuum pump, the most important lubrication points are generally the shaft bearings and rolling bearings. On oil-sealed pumps, the oil in the working section serves both lubrication and cooling. On liquid ring pumps, the maintenance needs of the mechanical seal and the bearings are assessed separately.

The user manual of each pump lists the lubrication points, lubricant types and change intervals. This information should be kept in a table as a shared reference for the field team.

The main lubrication points of a vacuum pump are the shaft bearings where the rolling bearings sit, the coupling connection and, if fitted, the gearbox. These points are the main connection places of the moving parts of the pump and are the parts with the highest need for lubrication. The oil type and interval given by the manufacturer for each point should be clearly recorded in the maintenance records.

Motor bearings should also be included in the lubrication calendar together with the pump. The motor bearings may need a different lubrication interval depending on the working conditions of the pump. The motor nameplate and the manufacturer's manual are the basic sources for setting this interval.

The coupling connection joins the motor and the pump shaft and may need lubrication. Elastomer couplings usually need no maintenance, but metal gear couplings should be lubricated regularly. Coupling lubrication should be carried out together with the alignment check.

On pumps with a gearbox, the level and condition of the gear oil should also be checked. Gear oil lubricates and cools the gears. The colour, consistency and contamination of the gear oil should be examined regularly and it should be changed when necessary.

Bearing Lubrication: Too Little or Too Much?

Over-greasing a bearing is as harmful as under-greasing it. Excess grease can cause heating inside the bearing and grease leakage. This means the lubricant spreads into the surroundings and the bearings become contaminated. Apply the quantity and interval specified by the manufacturer for every lubrication.

After lubrication, monitor the motor temperature and sound for several days. If a sudden change appears, check whether the quantity was too high.

The most discussed question in bearing lubrication is whether too little or too much grease should be given. Both too much and too little lubricant can damage bearings. The correct quantity must be set according to the bearing type, its size and its operating speed.

The result of giving too little lubricant is that the bearing surfaces are not sufficiently lubricated. Friction increases, the bearing heats up and over time surface damage called brinelling or pitting appears. The first sign of insufficient lubricant is a squeal from the bearing and an increasing temperature.

Too much lubricant, on the other hand, will fill the air spaces inside the bearing and make it harder for the rolling elements to turn. Excess grease causes overheating inside the bearing and the lubricant itself begins to break down. This shortens the life of the bearing and causes lubricant to leak out.

The correct method in bearing lubrication is to give the amount stated by the manufacturer at the set interval. If grease lubrication is used, care must be taken that the new grease displaces the old, and it should not be pumped in until excess grease comes out. After each lubrication the bearing temperature and sound should be checked.

Oil Checks on Oil-Sealed Pumps

On oil-sealed pumps, the oil level should be checked regularly through the sight glass. The level should sit between the minimum and maximum marks. When the oil darkens or gives off a bad smell, it may be time for a change.

When changing the oil, use the oil type and quantity specified in the catalogue. Mixing different oils can change the properties of the lubricating film and cause problems inside the pump.

The lubrication method changes with the type of bearing. Open bearings need frequent lubrication, whereas closed and sealed bearings may run for a long time without being lubricated. This difference directly affects the maintenance plan and a separate interval should be set for each bearing type.

In oil lubricated pumps, the oil check has a separate importance alongside the bearing lubrication. The oil inside the pump lubricates the vanes and provides sealing. A fall in the oil level leads to wear of the vanes and loss of vacuum.

The check of the oil in an oil lubricated pump should be made from the sight glass on a cold pump. The level should be near the middle line of the glass. The colour, consistency and smell of the oil should also be assessed at every check, and if something abnormal is seen, a change should be planned.

In oil lubricated pumps part of the oil may be lost over time through evaporation or leakage. Although this loss is accepted as normal consumption, a high loss may be a sign of leakage. Recording oil consumption regularly helps to notice this situation early.

Signs of Incorrect Lubrication

Signs of under-lubrication include metallic rubbing noise, rising vibration and heating at the bearings. Signs of over-lubrication include oil leaking from the body, dirt build-up on the motor winding and sometimes a wet appearance on the outer surface of the motor.

When these signs appear, first check the lubrication quantity and type. If the problem continues, the condition of the bearing should be assessed together with an authorised service team.

The signs of wrong lubrication are sometimes difficult to tell apart on their own. A rise in temperature, a change in sound, an increase in vibration and a squeal from the bearing are the most typical signs of a lubrication problem. Since these signs can have other causes too, they should be considered together.

A rise in temperature is the most common sign of insufficient lubrication. If the bearing surface is not lubricated, friction produces heat and the temperature rises quickly. Measuring temperature at the bearing point allows this sign to be interpreted correctly.

A change in sound is another important sign that lubrication has become insufficient. The friction and metal contact inside the bearing show themselves with a characteristic sound. At first this sound may be a slight hum, but over time it can turn into a severe squeal.

An increase in vibration can also be a result of lubrication problems. An unlubricated bearing produces more vibration while it runs, and this vibration spreads through the whole body of the pump. Vibration measurement can be used to monitor the condition of the lubrication objectively.

Tracking and Recording Lubrication

At every lubrication and oil change, record the date, the type of material used, the quantity and the observations made. These records are the best source of data for judging whether the lubrication interval is actually adequate.

Planning lubrication together with the maintenance calendar helps prepare the required materials in advance and reduces steps forgotten during maintenance.

Lubrication tracking and recording should be the most important part of maintenance. It should be recorded at which point, when, with which oil and in what quantity the lubrication was done. These records provide the basic information for testing the accuracy of the lubrication intervals and changing them when necessary.

In the record system a separate line should be opened for each lubrication point. The line should contain the date, the oil type, the quantity, the person who lubricated and the temperature and sound condition observed afterwards. This layout lets the lubrication history be followed from one place.

In lubrication tracking, temperature and vibration measurements should also be combined with the record. The temperature change after lubrication shows the effect of the lubrication and helps to set the correct interval. Over time this data allows the lubrication plan to be optimised.

In conclusion, lubrication in a vacuum pump is an operation that needs constant attention and regular recording. Lubricating the right point with the right oil, in the right quantity and at the right time clearly extends the life of the pump. Lubrication tracking makes this process measurable and manageable.