image You can read the whole article in the book:

Introduction to Medical Equipment Repair

The book also contains a chapter on preventive maintenance, with recommendations on how to perform the various tests.
Click here for more information.

Repair of Suction Pumps

by Frank Weithöner

A medical suction pump is a motor-driven device used to remove mucus, blood and other body fluids from a patient.
Suction pumps can be found in operating theatres, where body fluids, tissues and gases are removed during surgery. In maternity wards, suction pumps are used to clear blockages caused by blood or secretions in the mouth, nose or upper airways of newborn babies. Suction pumps are also used in other wards and in home care to clear patients' airways of blood, saliva, vomit or other secretions.
Suction pumps are portable or mobile units containing electric vacuum pumps. They are powered by mains electricity or rechargeable batteries.
The body fluids are aspirated from the patient through a catheter and plastic or silicone tubing and collected in a container attached to the outside of the device. The container can be easily removed for emptying and cleaning.

This large mobile suction pump has an additional spare collection container which is connected when the first one is full.

In hospitals with a central gas supply, there are often also connections for vacuum, so there is no need for suction pumps in the operating theatre. In remote areas of developing countries, mechanical suction pumps that function as foot pumps are still occasionally found.

A suction pump consists of the pump itself, the device that creates the vacuum, and a collection container in which the liquids are collected. The device and the container are connected by a short tube and a bacterial filter. Sometimes another, smaller container is connected in between. The suction tube to the patient with the catheter is connected to the second connector on the collection container. In between is a tube connector with a fingertip. The fingertip is an opening that the user closes with a finger to start the aspiration.
When switched on, the pump hums as a sign that it is running. The vacuum gauge on the unit will not show any vacuum because the patient tube is open. If you now close the connected tube with your thumb, the vacuum will build up. This vacuum can be adjusted using a control knob.
During operation, the operator should check the fluid level in the reservoir from time to time. The reservoir should only be half full and then emptied. If the reservoir becomes too full, a float valve will close and the pump will stop sucking.
After each use, all parts that have come into contact with liquids must be thoroughly rinsed under running water and then disinfected. The parts must then be allowed to dry properly before being reassembled. If this is not done, the bacterial filter will become damp during operation or the pump will even be damaged.
When reassembling, the user has to ensure that the float valve can be moved easily. The container lid must be screwed on straight and tight. The hoses must be connected correctly.
The bacterial filter should be replaced after each use. If the pump remains with the same patient, the filter only needs to be replaced every two weeks.

Common operating errors
The suction pump is not a complicated piece of equipment, so you would not expect any problems. But problems do occur. Here are some common mistakes:
  The lid is screwed on crooked. As a result, the collection container is not tight and there is
     hardly any suction power.
  The clear plastic of the collection container has become opaque and milky. The wrong
     disinfectant or the wrong dosage has been used.
  The bacterial filter has become damp. It has been washed during cleaning or the parts have
     not been dried properly. The unit has no suction power.
  The ball in the float valve is missing. The bacterial filter is missing. The inlet and outlet tubes
     have been mixed up. These are faults that go unnoticed until the reservoir overflows and
     liquid enters the pump. Corrective action: User training and regular maintenance.

Cleaning by the user
Each time a patient is changed, all parts that come into contact with the suction fluid must be cleaned and disinfected. These are the container, lid, overflow protection and tubing. The float valve in the lid must be disassembled before cleaning. Disposable items such as bacterial filters, fingertips and catheters must be disposed of. The surface of the device should be cleaned with a damp cloth and then disinfected for each new patient.
The user manual will tell you which disinfectants to use, at what concentration, and which parts can be autoclaved. Otherwise, the hospital's cleaning procedures apply.
After cleaning and disinfection, the parts must be dried. Ideally, tubes should be hung up.

In a normal water pump, the water flows through the pump. This means that parts of the pump come into contact with the water. This is not desirable in a suction pump. Body fluids can be infectious. After use, all parts would have to be laboriously cleaned and disinfected.
Therefore, an air pump is used to create a vacuum in an external collection container. This vacuum then sucks the liquids through a hose into the container. This separates the liquid container from the pump. The actual pump does not come into contact with the liquid and does not need to be cleaned and disinfected after each use.
Another advantage of a vacuum pump is that it can pump both liquids and air. For example, a centrifugal pump for liquids must always be filled with liquid in order to pump. If air enters the system, the liquid flow is interrupted and the pump stops pumping. A liquid pump cannot normally pump air.
Note!     The suction pump pumps body fluids, but it is not a liquid pump. It is a vacuum pump that sucks in air.

Functional description

                    The components of a suction pump.

The suction pump always consists of two parts, the technical part with the actual vacuum pump and the user part with the collection container and the suction hose. Both parts are protected from each other by a safety mechanism so that no body fluid can get into the pump. Only the collection container and the hoses come into contact with the patient fluid. The components on the user part are designed to be easy to clean after each use.
The technical part of the suction pump is located inside the housing and is connected only to the user part by a vacuum hose. The vacuum generated by the vacuum pump is indicated by a pressure gauge for negative pressure. The pump always runs at the same speed producing the maximum vacuum. As this is not always desired, a vent valve is fitted in the tubing. This adjustable valve allows more or less air to enter the system from the outside, which reduces the suction power.
The user side with the fluid collection container is open for easy access by the user. The container has two tube connections. The suction tube to the patient is connected to one of these. The other goes to the pump. However, there are always two safety mechanisms between the collection container and the pump to prevent liquid from entering the pump: a float valve and a bacterial filter.

Mobile and portable suction pumps are driven by a single-phase or universal motor. The pump itself is either a diaphragm or a cylinder pump. An inlet and an outlet valve ensure that there is always positive pressure on one side and negative pressure on the other. (For more information, see: Error: Reference source not found Error: Reference source not found)
The pump sucks air from the collection container. This container is made of plastic or glass. It has an airtight lid and another opening, the inlet. This is where the suction hose is connected. The pump creates a vacuum in the collection container, which causes the liquids to be sucked into the container.
In order to protect the suction pump and the personnel from contaminated liquid and air, the system is equipped with two safety mechanisms. Firstly, there is a float valve between the collection container and the pump unit. This valve is built into the lid. It closes the outlet of the collection container when the liquid level reaches the float. The vacuum connection between the pump and the container is interrupted and no more liquid can be sucked in.

A typical float valve. Sometimes the float is simply a plastic ball.

The float valve can be a simple plastic ball in a plastic cage that blocks the hose connection as soon as it floats and moves upwards. Instead of such a mechanical valve, other suction pumps use a water trap, an additional small glass container between the collection container and the pump. Still other suction pumps have two electrical contacts that act as a level sensor and a control electronics. When liquid comes into contact with the contacts, the pump shuts down.
In addition, all suction pumps have a bacterial filter between the float valve and the pump. This serves two purposes. Firstly, it protects the staff from contaminated aerosols when air flows over the liquid in the reservoir and is then blown out into the room. Secondly, the filter provides additional protection for the technical unit in case the float valve should malfunction. This filter is a PTFE membrane filter, which is also used in other medical devices, such as bacterial filters in oxygen concentrators.
Then there is another filter in the unit. This is connected to the pump outlet. It reduces the exhaust noise of the pump and is therefore a silencer.
There is an adjustable vent valve in the vacuum system, for example a ball valve. This allows the user to control the vacuum. By opening this vent valve, more air enters the vacuum system through the valve and less through the patient tube. The suction power in the patient tube is reduced. The possibility of pressure adjustment is necessary because different applications require different vacuum pressures. A connected pressure gauge shows the current negative pressure in mmHg, bar, psi or kPa.
The suction pump is switched on and off by the main switch, but the actual suction is controlled by the fingertip on the catheter. When the fingertip is open, air is sucked through the opening in the fingertip and no fluid is aspirated. When the opening is closed with the finger, the pump sucks through the catheter.

A fingertip is simply a tube connector with a hole that can be closed with the thumb.

Before you start with the repair:
  Note accessories such as collection container and power cable on the job card to avoid
     confusion later.
  Carry out a test run in order to confirm the fault. Make sure that the problem is really a fault
     and not an operating error.
  If you are not sure how to operate the unit yourself, consult the user manual.
  Wear disposable gloves when dismantling, repairing and cleaning.

A suction pump that is to be repaired must first be cleaned by the user. Even if this has been done, a suction pump can be very dirty inside if liquid has entered the pump. You should therefore wear disposable gloves when repairing and disinfect the unit before repair.

Note!     Always wear disposable gloves when working on suction pumps.

Locating the problem
The suction pumps should always come to the workshop complete with the collection container and connection hose, as leaks and damage are often found in these parts. Or even better, look at the problem on site and only take the motor unit to the workshop if it is faulty.
As always, we start a repair with a short test run. Connect all the parts together and check if vacuum builds up by closing the end of the hose with your thumb. The vacuum should be noticeable and the pointer of the pressure gauge should move. You should not hear any hissing leaks.
It should be possible to set a pressure of at least ­-0.5 bar (-50 kPa, -8 psi) using the adjustment knob. All suction pumps should easily reach this pressure. If this pressure cannot be reached, something is wrong.
If no vacuum builds up, you should disconnect the short connecting hose and test whether the pump itself works by closing the hose. If not, the unit must now be disconnected from mains and opened.


This suction pump has a single-phase induction motor with integrated piston pump. In the front is the silencer. In the background, inside the housing, is the suction hose with a T-piece for the inlet connector (right) and the adjustable vent valve (left).

Common problems
Common problems are a blocked or a leaking suction system. A blockage exists when the negative pressure rises even though the end of the tube is open. A leak is present when you close the patient tube with our thumb and the negative pressure does not rise or rises insufficiently.
Leakages are the main problem with suction pumps. Everything is possible: a missing lid gasket, a damaged vent valve, a tube not connected properly and others. But the problem is easy to troubleshoot. Close the patient tube and listen for a hissing sound. The internal pressure gauge will also tell you if you are on the right track.
It is not unusual that liquid gets into the actual pump. This can happen during suction if the float valve is not working properly and no bacterial filter is used or if the suction pump is transported with a full collection container. In this case, the entire pump must be dismantled and each part cleaned and disinfected.
This happens more often in developing countries, where suction pumps are often used without a bacterial filter. This is because spare parts and consumables are hard to come by. From a technical point of view, it is better to leave a used bacterial filter in the tubing system than none at all.
But the bacterial filter can also be the cause of the problem. If it has become wet during cleaning, it will also block the system.
Tube ends that no longer fit tightly on the connection nozzles need only to be cut off and they will fit tightly again.
If a tube has to be replaced, make sure that it is also suitable for suction pumps. They must have a certain wall thickness otherwise they will contract under the vacuum and block the flow.

Note!     Bacterial filters for suction pumps are usually identical to bacterial filters for oxygen concentrators and ventilators. Therefore, bacterial filters should always be kept in stock in sufficient quantities.
The pump may become stuck, especially after liquid has entered. Then the fault is probably due to a stuck piston.
The motor also become stuck if, for example, the bearings are corroded. It is also possible that the motor hums and does not run because the capacitor is defective. Determining whether a pump is stuck is easy. Just unplug the pump and try to turn the motor by hand. The easiest way to do this is to turn the impeller of the fan. (For more information, see: Error: Reference source not found Error: Reference source not found)

To test whether the pump or the motor is stuck or the capacitor is faulty, you can try turning the pump motor with your finger. This should be possible. Of course, the mains plug must be unplugged first!

Caution!     Always discharge motor capacitors before touching them.

After the repair
After repairing the suction pump, switch it on briefly before reassembly to see that it works and that nothing else is faulty. If this is the case, remove dust from the inside of the unit if necessary. Then screw the unit back together.
When the unit is reassembled, clean the outside of the unit with a soap solution. Do not forget to clean the mains cable and the accessories as well. After drying with a dry cloth, the unit can be disinfected with a spray disinfectant.
Now a test run should be carried out. The test run should last 10 minutes, or better 20 minutes.
Finally, the electrical safety test should be carried out as explained in the Maintenance section. When the test has been passed, you only need to fill out the job card and the suction pump can be returned to the ward. (For more information, see Error: Reference source not found Error: Reference source not found)

Caution!     Clean and disinfect your hands and your tools thoroughly after working on a suction pump.

Further literature
On Wikipedia you can find further articles about these topics:
  Suction (medicine)

image You can read the whole article in the book:

Introduction to Medical Equipment Repair

The book also contains a chapter on preventive maintenance, with recommendations on how to perform the various tests.
Click here for more information.