Fault Analysis Report for the 2X-70 Rotary Vane Vacuum Pump

Oil Draining, Internal Cleaning and Refilling Procedure

Table 1  Document control information

1  Purpose and Scope

This instruction defines the procedure for draining the used oil, cleaning the pump cavity without dismantling the pump, and refilling fresh oil on a 2X-70 two-stage rotary vane vacuum pump. It is intended for maintenance personnel who are qualified to work on rotating machinery and who are familiar with the pump and its oil system.

The procedure covers routine oil replacement under normal contamination and, where the drained oil is black, emulsified or heavily sludge-laden, repeated flushing. It does not cover major overhaul, that is, dismantling the pump cavity to remove the rotor, vanes and valves; that work is required only when ultimate vacuum has clearly deteriorated, sludge is thick, or the vanes are seized.

2  Oil Specification and Consumables

2.1  Oil specification

A mineral oil designated N100 (also written 100# mechanical vacuum pump oil, equivalent to ISO VG 100) is the grade normally specified for the 2X series, with a nominal kinematic viscosity of about 100 mm2/s at 40 degC. Commercially available equivalents include Huifeng HFV-A100 or HFV-M100, Great Wall No. 100 vacuum pump oil, and the Nanguang original NVO-100.

VG 68 oil should not be substituted: its lower viscosity reduces the sealing film at the vane tips and end faces, which impairs ultimate vacuum and increases wear. Oils of different brands or grades must never be mixed in the same sump, because additives and base oils of different composition can react and form sludge or emulsion.

2.2  Tools and consumables

Table 2  Tools, materials and service parts

3  Safety and Preparation

3.1  Safety precautions

Isolate the pump electrically before any work on the oil system and lock out the supply so that the pump cannot be started by another operator. The pump and its oil sump become hot during operation; allow the oil to cool to a safe handling temperature before opening the drain plug, while keeping it warm enough to flow freely.

Depressurise and isolate the vacuum system, and open the inlet to atmosphere before draining, so that no residual vacuum or process gas is present in the cavity. Used vacuum pump oil may contain process condensate, solvent vapour or contaminants from the evacuated process; handle it as industrial waste, do not discharge it to drains, and dispose of it through the site waste-oil route.

3.2  Preparation

Place the pump on a level surface with sufficient clearance below the sump for the drain container. Where the design permits, raise the motor end slightly so that residual oil collects at the drain port. Confirm that the correct grade of new oil and the required service parts are at hand before the pump is opened, so that the cavity is not left open longer than necessary.

4  Procedure

4.1  Step 1  Preheating the used oil

Run the pump with the inlet open to atmosphere for 20 to 30 minutes. Warm oil is less viscous and carries suspended sludge and condensate out of the cavity far more completely than cold oil. Do not run the pump under vacuum load during this step, as the aim is only to raise the oil temperature.

4.2  Step 2  Shutdown and isolation

Stop the pump, switch off and lock out the electrical supply, and allow the oil to cool sufficiently for safe handling. Position the drain container under the sump and remove the oil filler cap so that the sump can vent while it drains.

4.3  Step 3  Draining the used oil

Remove the drain plug and allow the oil to flow out completely. When the flow slows, turn the pulley by hand through a few revolutions so that oil and sludge retained in the cavity and in the oil passages are pushed out. Refit and tighten the drain plug after the port threads have been wiped clean; renew the sealing washer if it is hardened or damaged.

4.4  Step 4  Flushing the pump cavity

With the drain plug tightened, pour approximately 0.3 to 0.5 L of fresh N100 oil into the inlet port, then jog the motor for 5 to 10 seconds only and stop. Short jogging circulates the flushing oil without running the pump dry or hammering the valve plates. Drain the flushing oil through the drain port and inspect its colour.

If the drained oil was black, emulsified or heavily sludge-laden, repeat the flush two to three times until the oil coming out is visibly lighter in colour. Never flush with petrol, kerosene, diesel or solvent: these strip the oil film from the vanes, end faces and bearings, damage the seals, and can permanently degrade ultimate vacuum.

4.5  Step 5  Inspecting service parts

With the sump still drained, inspect the items that most often cause loss of performance. Clean the inlet filter element; a blocked element reduces pumping speed and raises the pump temperature. Examine the exhaust valve plates and the oil mist separator element for sludge build-up, cracking or breakage; heavy oil mist at the exhaust or oil carry-over indicates that the separator must be renewed. Check all sealing washers and gaskets exposed during the work and renew any that are aged.

4.6  Step 6  Refilling with fresh oil

Level the pump, then fill filtered N100 oil through the oil filler port at the top of the sump until the oil level reaches one half to two thirds of the sight glass with the pump stopped. The level rises slightly when the pump runs, which is normal. An overfilled sump causes oil carry-over and heavy oil mist at the exhaust; an underfilled sump starves the bearings and vanes and prevents the pump from reaching its specified ultimate vacuum.

4.7  Step 7  Test run

Refit the oil filler cap and reconnect the drive belt. With the inlet open to atmosphere, jog the motor briefly to confirm the direction of rotation is correct, then run the pump for 5 to 10 minutes and observe it: listen for abnormal noise, watch the oil level, and check the exhaust for excessive oil mist. If the pump runs smoothly, reconnect the vacuum line and return it to service; if noise, overheating or oil carry-over persists, stop the pump and investigate before putting it back on load.

5  Acceptance Criteria

The oil change is complete when the conditions in Table 3 are met.

Table 3  Acceptance criteria after oil change

6  Prohibitions

The following practices are not permitted in any oil change, regardless of how severe the contamination is.

1. Mixing oils of different grades or brands in the same sump.

2. Flushing or cleaning the cavity with petrol, kerosene, diesel, thinner or any other solvent.

3. Running the pump with the sump empty, or jogging the motor for extended periods during flushing.

4. Overfilling above two thirds of the sight glass in order to lengthen the service interval.

5. Reusing a hardened drain plug washer or refitting a damaged gasket.

6. Starting the pump with the inlet still connected to a process under vacuum immediately after refilling.

7  Service Intervals

The interval depends on the duty, not on calendar time alone. Table 4 gives the intervals normally applied to the 2X series.

Table 4  Recommended oil change intervals

Where the pump is taken out of service for an extended period, drain the oil, clean the cavity, refill with fresh oil for preservation, and blank off the inlet and exhaust ports to prevent ingress of moisture and dust.

8  Records

Record the date, operating hours at the time of the change, oil grade and quantity used, parts renewed, the condition of the drained oil, and the measured ultimate vacuum after the test run. These records allow the service interval to be adjusted to the actual duty of the pump and provide the basis for diagnosing repeated oil deterioration.

Appendix A  Bilingual Terminology

Table A.1  English and Chinese terms used in this instruction