Selecting a Vacuum Pump for Stabilizing
I get asked which vacuum pump is best for stabilizing every day so I decided to write this article to provide guidance. Vacuum pumps are like any other tool you purchase. You can go budget at the expense of quality or go quality at the expense of budget, it just depends on your philosophy on tool purchases and how much you think you will use it.
Types of Pumps
What type of pump do you need? There are really three main types of “pumps” commonly available, water ring pump, diaphragm pumps, and vacuum generators. Each work differently and produce different levels of vacuum. The closer you can get to 100% vacuum, the more air you can remove from your material. The more air you remove, the more resin you get back in and the better your material will be stabilized!
Single Stage Vs. Two Stage
When shopping for a pump you will see a number of specifications. Some are relevant for stabilizing and some are not! Typically, the first thing mentioned is the number of stages, either single stage or two stage. Two stage pumps basically have two rotors and two sets of vanes. The first stage generates a medium vacuum and the second stage processes the exhaust of the first stage to create a better vacuum. As a result, two stage pumps can produce a deeper vacuum than single stage pumps. However, the typical vacuum chamber, hoses, and fittings can not take advantage of that deeper vacuum! When you get to real deep vacuum, almost everything becomes porous. A typical vacuum chamber and hoses will be doing good to produce a 700-800 micron vacuum (more about microns later but lower is better).
A typical single stage pump is capable of creating a 75 micron vacuum where a two stage pump can typically create a 25 micron vacuum. However, if your chamber and hoses leak to the point that they can only get to 700-800 microns, the difference between a 75 micron single stage and 25 micron two stage pump is moot! All else being equal, save your money and buy a single stage!
CFM (Cubic Feet per Minute)
The next specification you will see is the CFM rating. This is how many cubic feet per minute of free air the pump will move. This measurement is made at the pump with nothing attached and drops off significantly as vacuum is created. The question always come up about how many CFM you need. For stabilizing, CFM is irrelevant. Once you get a vacuum chamber down to deep vacuum, maintaining that vacuum requires virtually no CFM. Even when pulling the system down to deep vacuum, CFM plays no part since the typical fittings and vacuum hoses used on a stabilizing system only allow around 1 CFM of air flow.
So, even if you have a 10 CFM pump, it is only going to be operating at 1 CFM anyways! Even if you could take advantage of the higher CFM by going with larger fittings and hoses, it would only help you get to full vacuum quicker. Instead of taking 30 seconds, it may only take 15! Add in the fact that you are going to be controlling the vacuum by slowly closing the valve on the chamber, this is not even any benefit. Higher CFM does NOT mean better vacuum and is unrelated in any way. Save your money on go with a lower CFM pump!
Different pumps will have different size motors. The size of the motor makes no difference in how much vacuum the pump will produce. It is best to just ignore the size of the motor.
I mentioned earlier that I would get to microns. Micron is a unit of measurement of vacuum commonly used in the US. The other typical measurement in the US is inHg or inches of mercury. Oil filled rotary vane pumps will typically show the level of vacuum they will generate in microns since that is the measurement most used in the industry, at least here in the US so that is what I will focus on. The micron scale is a very precise scale of measuring vacuum and ranges from 0 microns being perfect vacuum to 760,000 microns being no vacuum at sea level on a standard day. Therefore, the lower the micron rating, the deeper the vacuum the pump is capable of creating. Remember, however, that a typical vacuum chamber and hoses will never allow you to get lower than a 700-800 micron vacuum so this is not that important of a number. All oil filled rotary vane pumps I am aware of will produce at least a 100 micron vacuum, well lower than your chamber!
Budget vs Quality
When looking at vacuum pumps, you really only have two choice. You can buy budget or quality. All of the budget pumps are imports, usually from China. These pumps can be fine for casual use but unfortunately, they are not serviceable or rebuildable. If you happen to suck some Cactus Juice into your pump or the pump seizes due to other contamination, you pretty much have to just toss them and purchase a new one. Parts are not available and the critical internal parts are typically plastic so trying to disassemble them to clean them out causes damage.
Caring for your Pump
Assuming you take my advice and purchase an oil filled rotary vane pump, I thought I would give some tips on taking care of that new pump! If you read the owner’s manual, it will tell you to change the oil after every use. Remember, these pumps are made primarily for the industry where vacuum is used to remove moisture from lines before introducing refrigerant. In that use, it is necessary to change oil after every use to get rid of the moisture that contaminates the oil In stabilizing applications, if you follow my directions completely, you will not be contaminating your oil with moisture since you will be drying your wood properly before stabilizing! I typically change my oil after every 4-5 uses or when it starts to look dirty or milky when viewed through the site glass. Also make sure you ALWAYS start the pump with all valves open and ALWAYS open the valve to release vacuum to the chamber before shutting the pump down. NEVER shut an oil filled vacuum pump down while there is still vacuum in the chamber. It will cause oil to spit out the exhaust the next time you run it and cause premature failure of the coupler between the motor and vacuum mechanism.
Pump Brands, Prices, and Recommendations
Users lack brand awareness, pay too much attention to price and neglect to consider other aspects, such as product quality, function and verification of manufacturer information. If slightly attentive, you can realize that the vacuum pump manufacturer mentioned in the video can not be found, and the alarm should be loud.
I hope we have solved some of your problems about vacuum pump and provided a good starting point for you.