Fieldpiece Vacuum Pumps

While Fieldpiece Instruments has been an industry leader in HVAC tools and testing equipment for many years, within the past few years they have made a big splash in the world of vacuum pumps with the introduction of two groundbreaking models: the Fieldpiece VP55 Vacuum Pump and the Fieldpiece VP85 Vacuum Pump. Now a vacuum pump may seem like a pretty standard and more or less interchangeable piece of equipment, but there are several innovations that Fieldpiece has pioneered that make these pumps stand a head above the crowd. We're going to do a deep dive here on the mechanics and the science of vacuum pumps, which will help us understand just how powerful the new benefits that Fieldpiece has brought to the market really are. Spoiler Alert: It all comes down to the extreme importance of vacuum oil in evacuating AC systems. But more on that in a bit. Let's jump in.

To fully understand what gives the Fieldpiece Vacuum Pumps a leg up in the market, we need to go back to the beginning and run through the actual mechanics of pulling vacuum on a system. If this is review for some, we apologize, but it's always a good idea to get back to basics. It only ever helps to review the fundamentals.

So, what exactly is a vacuum pump meant to do? Well, to put it simply, a vacuum pump is intended to remove air and non-condensables (such as water) from an AC system. The presence of these in a system can cause inefficiencies and corrosion of internal parts, so it is essential that we remove them whenever we are about to charge a new system or after we've recovered refrigerant during a system repair (before re-charging).

We remove air and non-condensables by creating a vacuum with our pump. Now, a common misconception is that a vacuum pump produces suction. This idea probably owes something to the household vacuum and the images that it conjures up. But a vacuum pump doesn't actually suck anything. Technically speaking, in physics, a vacuum is a space devoid of matter. Of course, a vacuum pump doesn't produce a pure physical vacuum (but wouldn't that be something?). For working with refrigerants, a more approximate definition of a vacuum is a space with a gaseous pressure that is much lower than atmospheric pressure. Now we're on to something. That is the type of vacuum that a vacuum pump produces.

Gas or air always moves from a space of higher pressure to a space of lower pressure (you've heard "nature abhors a vacuum", which means it will try to fill that empty space with something). So, a vacuum pump creates a much lower pressure environment inside itself, which compels the air and other contaminants in the system to flow into the pump (and from there into the atmosphere). Incidentally, this creates a lower than atmospheric pressure (or vacuum) inside your AC system, which helps you to charge the system with new refrigerant properly (although charging a system is a subject for another article and another day).

Almost all residential and commercial vacuum pumps are composed of two distinct pieces – a motor and a compressor. The compressor is made up of a rotor and two vanes. Most high-quality modern vacuum pumps are dual-stage, which simply means they have two compression chambers. This design allows for a deeper vacuum pull, which we'll explain shortly. The purpose of the motor is to spin the rotor inside the compressor. That's all it does, and it's pretty simple. Basically, the more powerful the motor, the faster and more efficiently it will be able to spin the rotor. Why this matters will be apparent in a moment. Also, vacuum pumps have a fan that blows ambient air over the motor to dissipate heat and prevent any potential overheating malfunctions.

Now, if you will visualize the inside of the compression chamber, it is a large cylindrical space. Think of looking at it from the front, as a big circle. Inside this circle is a smaller circle that is set almost flush with the top part of the chamber, so it is off-center and leaves a lot more space in the chamber at the bottom. This smaller circle is the rotor. Coming out of opposite sides of the rotor are the vanes, which are spring-loaded and look, from the front, like rectangular poles. As the rotor spins, the vanes get pushed against the walls of the chamber and cut off the chamber into two separate sections. The first section receives air from the inlet port (from the system you're working on). As one vane passes the inlet, it creates a lower pressure space that causes inflow from the higher pressure area (the AC system). This space gets larger (thus drawing in more high air until the next vane passes the inlet. Now, this air we just drew in is cut off from both the inlet and outlet temporarily, causing the pressure to rise. By the time the vane reaches the outlet (exhaust), it is higher pressure than the exhaust port air and is thus drawn out the exhaust. This process goes on over and over until the system reaches the lowest pressure that the pump you have will allow you to pull. The Fieldpiece VP85 and Fieldpiece VP55 specifically are designed to pump a system down to 15 microns. An excellent rating and more than sufficient for residential and light commercial AC systems to be charged for full efficiency. A two-stage vacuum pump, like the VP85 and VP55, simply has two compression chambers. So instead of the first chamber porting to exhaust as described above, it goes through another compression chamber. The process is the same, just think of it like the situation above happening twice to the same portion of air pulled in.

So, what's all this got to do with oil? We mentioned above that the primary advantage of these Fieldpiece Vacuum Pumps (though there are many other great benefits and features) comes down to the importance of oil in evacuation and how Fieldpiece approaches this issue. You'll notice at the beginning of the last paragraph we italicized the word "almost" when talking about the rotor being flush with the wall of the compression chamber. This "almost" also applies to the action of the vanes pressing against the walls of the chamber. Vacuum oil is a viscous and thick liquid that is not permeable so that no air can pass through it. So, while vacuum oil serves the obvious function of lubricating the spinning motion of the vanes and rotor, many people do not realize that it is also creating an airtight seal between the vanes and the compression chamber wall. This sealing action is essential to creating the pressure condition for proper vacuum. When the oil is dirty or has condensation in it, it will allow air to pass through the moisture and dirt-filled parts. This condition creates an inefficient pressure differential and will severely affect the pump's ability to pull a proper vacuum. At the very least, dirty and moisture-filled vacuum oil will make your evacuation process slow as all get out.

The paragraph above explains why clean vacuum oil is so necessary to do your job right. Many people think it's not a big deal to have dirty old oil in their machines and then wonder why their pump runs terribly. You may have heard to change the oil before every use. This oil changing is a good practice, but not everyone will do it. But, should you decide to follow this sound advice, the Fieldpiece Vacuum Pumps make changing oil as easy as it can possibly be. Now we are going to run through the operation and features of the Fieldpiece VP85 and Fieldpiece VP55 in some more detail, with special attention to the oil replacement system, now that we have a firm grasp of all the technical and conceptual information.

When you set up your evacuation equipment, there are a few options for how to chain the various components. It is relatively commonplace to use a manifold and the respective vacuum line port between the pump and the system. However, while this will work pretty well, by far the most efficient and powerful way to perform a system evacuation is by hooking up the pump directly to the AC system on the vapor line. There is some difference of opinion on where to place your micron gauge. Technically the truest reading will come from the liquid line because it is the furthest point in the system and thus the best place to evaluate the vacuum level. You'll want to make sure you have fresh oil in your Fieldpiece vacuum pump before starting up. Flip the motor switch on, and you'll hear the pump start, and the backlit oil viewing window will light up. A quick aside: the Fieldpiece VP85 and VP55 both have a huge light-up viewing window for the oil chamber. In contrast to smaller, poorly lit sight glasses on standard vacuum pumps, this window makes it clear as day to check whether or not your pump oil is in good shape.

When you're starting out, you'll want to leave the gas ballast open, as this will prevent clogging up your oil early on with dirt and moisture that can be easily vented. Once you get below about 3000 microns, you'll want to close the gas ballast to ensure you get a deeper vacuum—no reason to have an extra open port at that point.

Now we come to the real powerhouse feature of these Fieldpiece pumps, the oil changing procedure. If you pop open the front cabinet of either the VP55 or VP85, you'll see the oil chamber has a valve that drains directly into a specially shaped empty oil container that is held in place by a spring-loaded platform. On top of the machine to the right is the port for adding new oil to the pump. The real kicker with these new Fieldpiece vacuum pumps is that you can change the oil in the middle of a job – while the pump is still running! This great feature means that if you pay attention to the quality of your oil, you can run the pump without ever having a loss of efficiency or a poor evacuation. You will want to change the oil somewhat quickly once you start the process to maintain your vacuum, although technically the pump will continue to run for about 3 minutes after the oil has been drained. The whole process should only take about 20 seconds, though (and it will run for 30 seconds without any drop in vacuum level), so you'll want to go ahead and swap it out quickly.

So, to change the oil on-the-fly, simply open the front compartment and open the valve on the bottom of the reservoir. It should take about 10 seconds to drain the oil into the empty bottle below. Now, having already opened the new oil port, simply take your backup bottle of Fieldpiece Vacuum Pump Oil pour it right in. Voila! It's really that simple. This process is the game-changing feature of the Fieldpiece Vacuum Pumps. Although it might seem like a lot of buildup here to get to this easy-to-use feature, it's vital to understand the importance and function of oil in evacuation, so you can appreciate how easy and efficient these pumps really are. With a standard pump, changing oil is a big pain, and changing mid-evacuation is out of the question. If your oil gets contaminated, you're out of luck. You'll have to pause or abandon the job to get it cleaned up or suffer through a painfully slow job. After all, the time when fresh oil is needed most is at the tail end of an evacuation, when pulling deep vacuum at low micron levels requires that airtight sealing action that only fresh oil can provide. The Fieldpiece vacuum pumps eliminate all the hassle of traditional pumps and make fresh oil a piece of cake. It's actually quite a revolutionary innovation in the world of vacuum pumps.

Let's take a quick look at some additional benefits of owning a Fieldpiece VP55 or VP85 and then wrap everything up. First off, you will notice that the design of the pump itself is not that of a standard vacuum pump. We think it looks quite a bit nicer to the eye, but there's also a functional reason. The wide, sturdy build prevents the pump from knocking around while running. It also accommodates a larger-than-standard cooling fan, to keep the pump running well and avoid the overheating danger we discussed above.

It may seem obvious, but the VP55 is a 5 cfm pump, and the VP85 is an 8 cfm pump. If you don't know, this number simply indicates the rate of flow through the pump. Simply put, the VP85 is faster, so your evacuation time will be shorter. However, the ultimate vacuum potential is the same, so the VP55 will get the job done if that's all that fits your budget, albeit slower.

The Fieldpiece VP85 Vacuum Pump does offer a few benefits that make is better than its little brother and merit the extra investment. Most significantly, the VP85 features a variable speed DC motor. The VP55 has a single speed AC motor and so would be subject to inefficiencies due to voltage drops in the power supply (typically an extension cord). However, the Fieldpiece VP85's DC motor allows the unit to function as full capacity down to 95 volts, which means that if you are getting low or inconsistent power from your extension cord, it's no big deal. This is a great peace of mind feature and also has another benefit wrapped inside it. Because the motor is variable speed, the VP85 is great for cold starts. When the weather is cold, vacuum oil is more viscous than normal, and if your motor powers right on to full capacity, it can end up working overtime, spinning thick oil around in the machine. The VP85 will run at the appropriate speed based on internal feedback, even when it's too cold out to straight run a standard motor. Finally, the VP85 has a convenient cut-out on its side for storing a spare, specially designed oil bottle. This cut-out adds another layer of ease to the mid-job oil replacement procedure. Instead of having to go back to a truck or tool bag, you've got the spare oil right onboard the pump.

Let's wrap it up now. If you've gotten this far with us, you're now basically an expert in vacuum pump theory (or at least know more than the average tech), and you have a good idea of the advantages that come with picking up either a Fieldpiece VP85 or a Fieldpiece VP55. Of course, if it's in the budget, we recommend going with the Fieldpiece VP85, as it's truly the cutting edge in residential AC evacuation. But at the end of the day, both pumps offer a simple way to do a superior job every time you evacuate a system, and you can't go wrong with either.