If you suspect your micron gauge isn’t working properly, try cleaning it. If the condition of the oil was extremely poor, more than one oil change may be needed to restore proper performance, but you should see an improvement after each oil change. If it does not, make sure your pump ballast is closed, ensure all caps and fittings are tight, change your pump oil, and then try again. The easiest way to test your gear is to start with the micron gauge connected to the pump only and see if it pulls down to under 50 microns in a few minutes. A pump that isn’t working properly and will not easily pull below 50 microns when isolated.Technicians who use the “30-minute vacuum, and let it rip” approach instead of proper measurement.

This can interfere with the micron gauge readings. The refrigerant can be pulled out of the system as well as released from the oil during evacuation. Refrigerant sensor interference, which can occur if the system previously had refrigerant in it.Some new hoses begin to off-gas when placed under deep vacuum. If the vacuum hoses have been used with refrigerant, they can contain contaminants or moisture. These include small hoses, longer hoses than necessary, valve cores, hose core depressors, manifolds, ¼-inch pump ports, and anything else that inhibits maximum flow. Because vacuum occurs at a maximum pressure differential of 14.7 psi, all restrictions can slow down the process. Common culprits are hoses, manifolds, joints, or flare fittings. The greater challenges that prevent proper vacuum are: The physics of evacuation are quite different from charging and pressure testing.Īn evacuation rig includes dedicated large-diameter vacuum hoses, core removal and depressor tools, and a vacuum gauge, and it is much more effective for evacuation than the tools we use for charging and pressure testing. The largest pressure differential during evacuation between the pump and the system we’re connecting to is 14.7 psi when we start evacuating, and as the pump pulls the system down, this pressure differential falls quickly at first and eventually reaches almost zero.Īny restrictions in the path between the pump and the system will greatly reduce flow rates during the evacuation process, resulting in significantly longer evacuation time. A bigger pump won’t result in a large pressure differential to overcome the restrictions like the 500 psi regulator did when we positively pressurized the system. The goal is to reduce the system pressure from 14.7 psia (760,000 microns) to as close to zero as possible - but we have to accomplish that using a pump that’s limited to 14.7 psi difference at most.Īn absolute pressure of zero or negative can’t be achieved, so the pressure at the pump intake is higher than zero no matter how big the pump is. Here’s why evacuation is different, and why removing restrictions and using large hoses is important. VACUUMING AN AMMONIA CHILLER: Even very large systems can be For instance, if we use a nitrogen regulator set to 500 psi for a 300 psi pressure test, we start pressurizing with a 500 psi pressure differential and finish pressurizing with a 200 psi differential. When pressurizing a system, we can achieve a high flow rate to bring the pressure up quickly by raising the pressure at the source well above the destination to overcome these restrictions. It’s the dehydration portion that requires a tight system and a deep vacuum, and it can be hard to accomplish without good practices.Ī charging manifold - typically small-diameter, ¼-inch charging hoses - and valve cores all impose restrictions to flow. The initial degassing stage generally happens quickly and easily. Then, during the dehydration stage, it boils off any liquid water from inside the system by decreasing the pressure to below the vapor pressure of water at the ambient temperature. This is referred to as the “degassing stage.” The lower the pressure in the system in microns, the deeper the vacuum below atmospheric pressure.Įvacuation accomplishes two important tasks.įor starters, it removes air and any other vapor from inside the system. We use a vacuum pump specifically designed for this, and we measure the vacuum in the microns of mercury pressure scale (micron) using a vacuum gauge. Pulling a vacuum on the system is simply removing matter (mostly air and nitrogen) from inside the system so that the pressure inside drops below atmospheric pressure. The atmosphere all around us is pressurized to around 14.7 psi (at sea level). We’ll make some recommendations that may differ from the methods you are accustomed to, but first, let’s cover what evacuation is and what it does. Once the repair or installation is complete and the system is fully assembled and pressure tested, it is time to connect the vacuum pump and evacuation rig.

Evac vacuum