Rotary Vane Vacuum Pump – Maintenance

Tips for maintaining your vacuum pump:

Best indicator for vacuum pump performance is a reliable digital vacuum gauge.

Having a vacuum gauge on your pump will allow you to figure out when the pump needs to have an oil change or be taken in for repair. Checking the pump’s ultimate depth is advantageous to do prior to each run to ensure a successful distillation.

When doing cannabinoid distillation with short path, I always shoot for an ultimate vacuum of 10 micron (0.010 torr) or better when running the pump “dry” or separated from the system. Be wary of how you measure this number – best way is to find a gauge with the same coupling size as the inlet port for your pump. IE: if your pump has a KF25 inlet, connect a gauge which has a KF25 connector. Avoid vacuum lines when possible as the turbulence caused by the bottleneck will yield inaccurate results. Keep in mind also that not all gauges operate the same. My experience with Digivac KF25 Bullseye gauges for example showed a 25-26 micron reading on a freshly changed Edwards E2M28. My Instrutek KF25 Stingers however, showed 4.9 micron on the same pump after a quick switch-over. The important thing to consider here regardless of which gauges you use is to determine and know the baseline depth for your pump when it is clean. If you can get back to the same baseline numbers after an oil change, you know you are doing proper maintenance on your pump.

Why do we need to change the oil?

During the run, especially during the distillation of high volatiles/solvents/terpenes – you may notice that your pump read-out is much higher than what it can achieve when isolated from the system. This is a sign of vapors from the boiling flask bypassing the cold trap. It is for exactly this reason that your pump oil will need to be changed frequently in order to stay at peak performance.

How do you know if it’s time to change the oil before you start a distillation? Start your pump and isolate it from the system with only the vacuum gauge and give it 10-15 minutes to warm up. If it doesn’t reach, it’s known ultimate vac level, within that time period – its time to change the oil. Keep reading.

Step – by – step

The following SOP will outline the full maintenance steps to changing rotary vane vacuum pump oil and maintaining its longevity as well as determining its ultimate vacuum (especially if you don’t know what it is).

  1. Isolate the pump from the system or detach from your system manifold – attach just a digital vacuum gauge directly to the vacuum port.
  2. Start the pump and allow it 10-15 minutes to pull a deep vacuum on the instrument – notate the reading.
  3. Open the ballast and notate the depth once the reading stops climbing. Allow the pump to run this way for 1-2 hours with the ballast open.

You will notice the pump will be very hot upon your return – this is normal. Your vacuum reading should have gotten deeper. Notate the number with the ballast open, close it, and notate that number.

  1. Now you can shut off your pump and immediately change the oil while the machine is hot. Use protective equipment and drain the oil into a pan or some other kind of container. Its best to have the pump elevated at an angle as sediment from the inside of the oil reservoir is allowed to flow out.
  2. Once all the oil has drained, tip the pump to allow all the remaining sediment and leftover drops of oil to leave the reservoir and put the cap back on.
  3. Fill ¼ with fresh oil and turn the pump on. Allow the pump once again 10-15 minutes to attain deep vac and record the reading.

If you are still not satisfied with your ultimate vacuum depth, consider buying a cleaning agent or flushing fluid to add into the reservoir. Run pump for duration as instructed and drain as before. This is like putting oil fuel cleaner into your gas tank of your car.

If for some reason your pump is having trouble maintaining vacuum or can’t achieve a previously attainable ultimate vac, this should be a sign that something is wrong. A rebuild may be required.

What does the ballast do?

Opening the gas ballast allows air into the oil reservoir which makes the pistons work harder to drive the motor – this generates more heat which helps purge the vacuum oil of water, certain volatiles, and terps (hence the smell). The additional heat also loosens up the caked-up garbage on the pistons and the walls of the oil reservoir.  Therefore, you should do your oil change immediately after shutting the pump off after a long period of operation while contaminants haven’t had a chance to settle and cool.

You may opt to open the pump’s ballast during the terpene portion of the run to allow the contaminants to leave the oil reservoir in the form of a vapor – warning this will make your lab very stinky. Most vacuum pumps come equipped with an optional oil mist filter – these filters have an exhaust port to which you can attach a hose and plumb to exhaust ventilation.

Exhaust & Mist Filters

Many of the pumps we use will come with a mist or exhaust filter. Their purpose is to limit the odor coming out of the pump and prevent oil mist from diffusing into the lab. As they accumulate oil, most will have a sight window with an indicator for replacement or drainage. Keep them clean and don’t cover them!

Make sure that you are not restricting the exhaust flow because this may pop the seal of the pump and you will need to bring it in for repair. The pumps need to be able to breath – they can hold a tremendously deep vacuum but even a little bit of pressure build-up and you will have a dud before long. It is for this reason that you should keep an eye on your mist filter and make sure the oil it’s catching doesn’t accumulate above the threshold or it will “drown” the pump. Drain or change out the mist filters as needed on a regular basis.

Dealing with stinky exhaust

The best way to avoid breathing in “fishy pump terps” in your workspace is to plumb the exhaust outside, but sometimes this isn’t an option. Another cool trick is to attach a tight-fitting hose to the pump exhaust and submerge the other end in a bucket of water + dawn liquid dish soap. The unpleasant smells will become trapped by the heaviness of the soap + water mixture and the resulting exhaust fumes will smell like dawn soap vs. degraded terpenes.


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