Ultimate Guidance of Screw Vacuum Pump

This instruction manual describes the operation and maintenance instructions and precautions for LG series/LGB series screw vacuum pumps. It is strongly recommended that personnel who operate or maintain the screw vacuum pumps shall read this instructions carefully before operation and maintenance, in order to extend the service life of products.

What is Screw Type Vacuum Pump?

LG series screw vacuum pump adopts four stages of equal guiding range rotors, and LGB series screw vacuum pump adopts four stages of variable guiding range rotors. These two series of screw vacuum pump’s main, driven rotor use the same outer profile line, the opposite direction of rotation, the meshing clearance is uniform, the meshing line is closed, the sealing is excellent, and the pumping efficiency is high.

The screw vacuum pump sucks gas through the main and driven rotor mesh rotation to make the closed space of the suction section become larger. when the gas is sucked into the pump cavity, as the pump continues to run, in the main and driven rotor spiral mesh rotation, the closed space from the inlet end to the exhaust end, the pressure rises steadily, and there is no intermediate exhaust phenomenon.

When the closed space is connected to the exhaust port, the gas in the exhaust channel backflushes into the pump cavity, causing the gas pressure in the pump cavity to rise, the temperature to increase, and bringing airflow noise. As the pump continues to operate, the volume of the enclosed space begins to gradually become smaller, and the gas in the pump chamber is continuously discharged.

This series of screw vacuum pump has no oil lubrication in the pump chamber to obtain a clean and dry vacuum. Screw vacuum pumps need anti-corrosion treatment when pumping corrosive gases.

What You Should Know Before Pump Operation:

Safety Notes:

1. Do not put too much weight on the pipes attached to the pump body.
2. Please do not start the equipment without a coupling cover, wrong start rotation direction will damage the equipment.
3. Do not run the equipment when the air inlet end is directly exposed to the atmosphere.
4. Please note that when doing any maintenance on the pump, be sure to disconnect the power to the vacuum pump first.

What Is Basic Structure Of Screw Vacuum Pump

At the same time, the little flowing lubricating oil can not effectively cool the gears and bearings, which will affect the service life of the vacuum pump and even malfunction. The oil chamber of the vacuum pump is equipped with a special cooling system to cool the lubricant.

Therefore, when the pump is under maintenance, please check the oil level and the condition of oil contamination regularly to decide whether the oil needs to be added or replaced.

Cleaning Screw Vacuum Pump Can Maintain Pump Performance

Cleaning Process:

• Cooling Purge: Cooling purging is used to cool the rotor and pump body. During pump operation, a cooling purge is required to cool the compression heat generated by the exhaust gas. The gas enters the pump chamber through the inlet port, where it is compressed by the rotor rotation and transferred to the discharge end, where it is heated by the heat generated by the compression.
• This heat can reach 100-200°C at the discharge end, so we need to use a cooling purge to reduce this temperature. In most cases, we use dry, clean air as the cooling purge substance, which is our standard purge substance. When using atmospheric air as the purge substance, an air filter is required at the inlet end. Cooling purge will take up the pumping speed, so that the actual effective pumping speed of the vacuum pump decreases, the larger the purge volume, the more obvious the effect.
• Purge substance:
  • Standard: Atmosphere through air filter.
  • Use of heat exchanger: Recycling of cooled exhaust gas using a heat exchanger.
  • Use of nitrogen or inert gas as a purge medium.
• Cleaning and purging: This series of screw vacuum pumps adopts high precision screw rotor and pump body, the pump meshing clearance is small, so it is necessary to clean the inside of the pump chamber before the screw pump stops working. Clean purging is especially important when pumping corrosive/toxic gases or viscous substances such as resins.
• When pumping corrosive/toxic gases, the residual gas will corrode the surface of the rotor and the pump cavity, making the pump’s meshing gap larger and leading to a decrease in the performance of the vacuum pump, which can cause the pump to fail in serious cases.
• When pumping viscous substances such as resin, the viscous substances will be adhered to the surface of the rotor or pump chamber after stopping the pump, making the pump meshing gap smaller and making the pump operation less stable, which can lead to vacuum pump jamming in serious cases.
• Before the pump stops working, close the main valve at the inlet end, and then fill the inlet with dry air or nitrogen to purge the inside of the pump cavity, and the purging time can generally be chosen from 10-15 minutes. The larger the inlet volume of the blowing medium, the higher the inlet pressure, the better the blowing effect, the inlet pressure generally does not need to be higher than atmospheric pressure.
• If the normal cleaning and purging can not effectively remove the harmful substances in the pump cavity, you can use steam or other clean gas as the purging medium for intensive purging. After the intensive purge is completed, a general cleaning purge is required to remove any residual steam or other cleaning gases from the pump chamber.
• Steam purge If a screw vacuum pump has not been used for a long time and stalling or overloading occurs when the pump is restarted, do not force it to start and run, and be sure to steam purge the screw pump according to the following steps.

Steam purging is required after processing the following substances: organics, monomers, polymers, resins, etc.

Steam pressure: approx. 1kg/c㎡G

Purge process: Close the suction valve and open the discharge valve or the discharge valve of the silencer/separator; Steam injection via pump suction path or inlet connection valve for 1-10 minutes (depending on the substance to be treated); Remove the back cover of the motor, turn the motor fan by hand to see if it runs smoothly, note that you cannot start the motor; When the pump runs smoothly, steam injection can be stopped. Then, start the motor and see if the pump runs normally.

If satisfactory results are still not achieved, the above steps can be repeated 2-3 times.

How to Operate the Screw Vacuum Pump

Installation Requirement

• Location: The vacuum pump needs to be installed on a clean, flat, hard foundation, either a concrete foundation or a metal frame. The foundation must have enough strength, fully consider the weight of the vacuum pump and the bearing area of the foundation, so that the vacuum pump will not be stressed due to the deformation of the foundation, which can lead to distortion and deformation of the vacuum pump when the force is serious, and destroy the internal structure of the vacuum pump, which is very easy to make the vacuum pump fail in operation, and even lead to irreparable damage of the vacuum pump.

If the vacuum pump is to be used outdoors, verify that the motor and other components are suitable for outdoor use.

The installation position of the vacuum pump must be designed to ensure that there is enough space for repair and maintenance of the equipment, so as to facilitate regular inspection, daily maintenance, as well as the disassembly and reassembly of the equipment.

If there is a vibration source near the installation location of the vacuum pump, vibration isolation devices must be designed, such as the opening of vibration isolation grooves, etc.

A groove of 5 to 10 cm should be left around the foundation to prevent staining of the plant when oil or water is released.

• Installation: The pump must be cleared of all dust and dirt on the pump before use, the pump room must always be kept clean and the ambient temperature should be within the range of 5-40℃.

When the vacuum pump is installed, the level of the foundation must be calibrated using a leveling tape, and the level error should be less than 0.5 mm/m. When the base error is too large, you can use a pad to assist in calibration. When using the pad iron, the force area of the foundation is reduced and the strength of the foundation needs to be recalibrated.

If there is vibration in the piping connected to the vacuum pump, bellows can be used to isolate the transmission of vibration.

How To Connect The Screw Vacuum Pump?

• Main Pipeline:

Clean the inside of the suction and discharge pipes to remove rust, dust and foreign objects, etc. And at the beginning of the operation of the screw vacuum pump, the suction inlet is equipped with a filter, and regular checks are made to ensure that the filter leaves enough channel area so that the filter is not sucked into the pump cavity, causing damage to the vacuum pump. After the vacuum pump has been running for a period of time, the screen can be removed after confirming that there are no more large hard objects in the pipeline.

It is recommended to use flexible connections, such as bellows, rubber hose, etc., at the suction and discharge ports, which can reduce unnecessary load on the pump body.

Be sure to install a non-return valve at the suction or discharge port so that the pump does not reverse the pumping. If the customer is unable to install a check valve, at least a gate valve needs to be installed and ensure that it is closed before stopping the pump.

If there is condensate in the pump discharge pipe, a recovery tank can be placed under the pump so that the condensate can be collected during pump operation and discharged through the discharge valve.

Note that a drain valve needs to be installed at the front of the condenser to collect condensate gas.

The inlet pipeline should be very tight, even a small leak will affect the vacuum level, the inlet pipeline should be as short as possible in principle, with few joints and elbows, and the pipeline connected to the pump should not be smaller than the pump diameter.

• Cooling water pipeline

For this series of screw vacuum pumps, the cooling system adopts direct water cooling for the end cover, side cover and pump body. The cooling water pipeline within the vacuum pump has already been connected, customers only need to connect the water inlet and the discharge pipeline to use, pay attention to the cooling water needs to follow the principle of the low position in, high position out. A valve on the cooling water inlet pipe shall be installed, which can adjust the water volume.

When the screw vacuum pump is running, the temperature of the rotor can reach up to 200℃, reduce the cooling water appropriately when running to keep the pump body at a higher temperature, For example, 80-90 degrees Celsius. It helps to reduce the temperature difference between the pump body and the rotor and increase the clearance between the pump body and the rotor, thus improving the operating stability of the vacuum pump. In addition, when pumping substances containing condensable gases, the cooling water can be appropriately reduced to keep the vacuum pump at a higher temperature, which can effectively reduce the condensation of gases in the pump chamber.

What You Need To Prepare For Start Up?

• Remove the dust from the pump, and make sure the pipe is clean and thorough, with no welding residue left inside.

• Check that all suction and discharge pipes and cooling water pipe ports are properly tightened and that all pipes are installed correctly.

• Refuel to the red dot on the fuel gauge. If the oil is too low, the gears and bearings will seize up. If there is too much oil, the temperature will rise excessively, causing gear noise or effects on other components. Please take care to keep the oil level at the red dot of the oil gauge for a long time.

Please configure the cooling water volume according to the requirements.

How To Operate The Vacuum Screw Pump?

1. Open the suction valve, Start the vacuum pump under no load condition to check the rotor steering and observe the motor fan steering. Run for 20-30 minutes under no load condition to check for abnormal vibration or heat generation. If so, stop the machine and look for the cause. In most cases, the cause is usually incorrect installation or not properly positioned. Other times it is due to a lack of lubricant.
2. When the pump has been running under normal load for 2-3 hours, please check the temperature and vibration of each part.
3. Observe the amperometer during operation. If any irregular condition is found, stop the pump immediately and find the cause. Common causes are collision between the rotor and rotor or contact between the outer ring of the rotor and the inner surface of the pump.
4. All of our pumps have been tested in this area. Nevertheless, the condition of the pump needs to be closely monitored, after all, the pump has been reinstalled on site.
5. Precautions during operation: Check the temperature of the bearings and lubricants as well as the cooling water. Keeps the pump working within the design range.

How To Stop The Screw Vacuum Pump?

1. Close the main valve on the inlet side.
2. In the event of corrosive gas suction, be sure to perform cleaning and purging before stopping the pump.
3. Turning the pump off by turning off the motor.
4. Turn off the cooling water system.

If there is severe cold icing, open the drain valve to remove the cooling water from the pump to avoid freezing and cracking of the vacuum pump.

How To Lubricate The Screw Vacuum Pump?

Use good quality, high-grade petroleum products including antioxidants, anti-corrosion agents, ultra-high pressure additives, and other components (do not use lubricants containing water, sulfate resin, or tar components), and factory standard 100# vacuum oil.

Turbine oil (ISO46) is available on the market and can meet the needs of a wide range of products for this type of pump.

The following brands are the recommended types of lubricants for bearings and gears.

• Lubricant：BP， Energol THHT 46/THB 46 / Regal R&O 46 / Shel, Turbo T 46 / Mobil, DTE oil medium or, equivalent.
• Oil esters: Almasol 1262 / G 40M (SHINETSU) /JFE 552 (KLUBER) / Arcanol L74V (FAG)

How To Guarantee Pump Performance?

During operation, the temperature rises according to the compression ratio. If the temperature rise is partial and very hot, it is abnormal. Possible reasons are that there is a problem with the cooling water supply or the cooling system is not opening, the rotor is rubbing against the pump body or a foreign object has entered the pump.

In this case, the pump must be stopped immediately and the cause checked. In some cases, the rotor and pump body may have corroded over a long period of operation, resulting in a larger clearance between these parts, a return of the discharge gas to the suction port, and a reduction in suction capacity compared to the original design capacity. In this case, the pumping capacity will drop significantly and it is necessary to stop the operation, measure the error and consider corrective measures.

Abnormalities can be detected immediately by routine inspection of the pump body, bearing temperature, vibration and noise. Therefore, a daily routine check of the pump is highly recommended.

The collision between the rotor and rotor or the contact between the outer ring of the rotor and the inner surface of the pump can be heard by placing a stethoscope on the outer surface. Therefore, it is also important to pay attention to the sound made by the pump.

In cold areas, when the pump stops, drain the cooling water to avoid damage to the pump body and side cover after the water freezes.

How To Carry Out Inspection and Maintenance

Daily Inspection Program:

• Check the oil gauge: too much or too little lubricant can damage gears and bearings.
• Check if the cooling water is sufficient.
• Check the temperature of the back cover and front cover. Use a suitable thermometer to measure them, using a surface thermometer will be more convenient.
• Check the suction and discharge end pressures. Measure the pressure to b ensure that the pump is operating within the range allowed by the specifications.
• Check the motor load. Note that an increase in motor load is often indicative of an abnormal condition.

Monthly inspection items

• Check the color of the lubricant. If the color of the oil becomes dark, replace the lubricant.
• Check the oil volume. If the oil decreases a lot, please check the seal structure inside the pump.

Quarterly inspection items

• Check the cooling water flow and color. If abnormalities are found, clean the cooling water jacket and water lines.
• Check the Grease on the rear end cap and add more if necessary.

Semi-Annual Inspection Program

• Check the pump connection line.
• Front end cover lubricant replacement
• Replace rear end cap grease.

Annual Inspection Program

• Check the vacuum pump internal dynamic seal.
• Check the internal rotor and pump body. Remove the suction pipe at the inlet end to check the condition of the internal rotor and pump body.
• Check the gears. Open the front cover to check the condition of the gears.

Screw Vacuum Pump Maintenance Checklist

How To Make Assembly of Screw Vacuum Pump

Assembly Notes:

1. When assembling, please take care to check for old or damaged parts. In particular, damage to the joints or mating areas will seriously affect the results of the assembly. Therefore, it is very important to carefully inspect the joints or mating places for wear or damage, and replace or repair them if found.
2. Clean the bearings with light oil, then lubricate. Any time you handle bearings, use clean tools and wash your hands.
3. Dust and oil the mating parts with a soft cloth and cleaner. Molybdenum disulfide is recommended for tight fitting parts, as these parts are difficult to remove once rusted. Assembly will be more difficult than disassemblyy. For tapered parts of gears, clean the surface thoroughly with a soft cloth and detergent before installation.
4. Use the same thickness as the old packaging to pack the new packaging.

Common Problems and Solutions

If the fault is still not eliminated by the operation of the above tips, the problem may be due to the operating conditions of the pump. In this case, please contact us and indicate the application information.

What Is The Daily Operation Checklist of Screw Vacuum Pump

Routine inspection of recommended wear parts, including all seals, bearings and various other parts that are not reused after routine disassembly. These parts can be ordered as a package by ordering a repair kit or purchased individually.

Please Feel Free To Discuss Any of Your Inquiries with us.