pump-down is the English term for the gas collection maneuver, which is applied in many refrigeration systems. This maneuver is carried out automatically, using electromechanical and electronic devices. Individuals who are not familiar with refrigeration and have heard the term “pump-down” may be very curious about it. If this is your case, in this post, you will be able to understand precisely what this maneuver is about. Additionally, you will comprehend its importance in industrial and commercial refrigeration systems.

What is pump down?

Pump down is an automatic maneuver to stop the compressor after collecting the refrigerant from the evaporator and the suction line. This way, all the refrigerant from the low-pressure side of industrial refrigeration systems is evacuated before stopping the compressor.

Except for emergencies, the refrigeration system compressor can be stopped when the temperature of the cold room reaches its set value. On the other hand, the compressor can also be stopped by an operator due to maintenance activities. In all these mentioned cases, the pump-down maneuver is used.

Importance and advantages of pump down

The pump-down maneuver protects the compressor from the accumulation of liquid refrigerant in its crankcase. Thus, serious damage to the compressor due to the suction of refrigerant liquid is avoided because a compressor only compresses gases.

Furthermore, pump-down protects the evaporator and the other components of the low-pressure side from overpressure. Additionally, with the refrigerant gas collection maneuver, the defrosting process of the evaporator becomes more efficient and faster. That is, the defrosting electric resistance will no longer have to waste energy heating the refrigerant gas.

How is pump-down implemented in industrial refrigeration systems?

After all the aforementioned, it is necessary to explain clearly how to implement pump-down in a refrigeration system. The gas collection maneuver is basically carried out using a solenoid valve and a low-pressure switch. Next, we will explain what these components are and how they work to perform a pump-down maneuver.

Solenoid Valve

The solenoid valve is an electromechanical device that opens or closes the passage of a fluid through it completely. It consists of a solenoid and a valve body.

The valve is controlled by a voltage signal applied to the solenoid, which creates a magnetic field that moves the valve plunger. When no voltage is applied to the solenoid, the valve remains tightly closed. However, when voltage is applied, the valve opens the passage completely.

To implement pump-down, a solenoid valve is mounted on the piping that supplies refrigerant liquid to the expansion valve and the evaporator. This way, the flow of refrigerant to the refrigeration system’s evaporator is fully controlled.

Low-Pressure Switch

The low-pressure switch is an electromechanical or electronic instrument that detects the pressure of a substance in liquid or gas state. This substance can be contained in a vessel or circulating through a pipe. The pressure detected by the pressure switch is internally compared to a preset or adjusted value to activate a set of electrical contacts.

It is important to note that the low-pressure switch is a device that activates or deactivates according to a differential curve. That is, if the pressure increases from zero to the set value, the pressure switch will actuate its electrical contacts at that value. But if the pressure begins to decrease, the pressure switch will remain activated even if the pressure is below the set value. This is known as pressure differential. For example, a pressure switch may be set at 15 psi with a differential of 5 psi. This means it activates at 15 psi but deactivates at 10 psi (15 – 5).

To implement pump-down, the low-pressure switch is mounted on the refrigerant suction line of the refrigeration system compressor. This way, as long as there is a certain pressure in the suction line, the pressure switch will keep the compressor running. However, when the refrigerant pressure drops below the preset value, the pressure switch will shut off the compressor.

How does the refrigerant gas collection maneuver work?

After understanding how the solenoid valve and the pressure switch work, it is easier to comprehend how they control the refrigeration system. For example, after a shutdown, when the refrigeration system is activated, the compressor does not start immediately. This is because the refrigerant low-pressure switch detects that there is not enough pressure, preventing the compressor from starting under vacuum. However, the solenoid valve activates immediately to inject refrigerant liquid into the evaporator.

When the refrigerant pressure at the outlet of the evaporator and in the suction line exceeds the value set on the pressure switch, the compressor starts. That is, the refrigerant low-pressure switch starts the compressor by activating its electrical contacts.

If the refrigeration system stops due to reaching the cooling temperature or for maintenance, the solenoid valve closes immediately. On the other hand, the compressor remains on as long as the pressure switch detects a minimum pressure (set value – differential). When the pressure drops below the minimum, the pressure switch orders the compressor to turn off. This way, as much refrigerant as possible is collected from the evaporator and suction line before stopping the compressor.

Are you experiencing any issues with the evaporator or condenser in your refrigeration system?

If you notice cooling deficiencies in your refrigeration system or suspect malfunctioning of your evaporator or condenser, you can rely on Intersam. We specialize in manufacturing evaporators and condensers for all types of industrial and commercial refrigeration systems. The effectiveness of pump-down maneuvers, as well as other operations, also depends on properly designed, manufactured, and installed evaporators and condensers. If you encounter any issues, do not hesitate to contact us.

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