If you've been told that your pump is the source of dissolved oxygen (D.O.) pickup, you're not alone. Pumps are often blamed when D.O. levels increase during product transfer, but the reality is more nuanced.
A simple rule of thumb is: "a pump moves what it receives."
A pump does not create air within a properly sealed liquid system. If air is detected downstream of the pump, it has typically entered the line before the pump through suction-side leaks, poor suction conditions, inadequate purging, or product entrainment. The pump simply moves the air that has already entered the system.
The discharge side of the pump is a high-pressure point, typically above atmospheric pressure. A damaged fitting or gasket there will result in liquid leaking out rather than air leaking in.
Unlike the discharge side, where liquid pressure pushes outward, the suction side can operate below atmospheric pressure. This means a tiny leak may pull air in because the suction side may operate below atmospheric pressure (negative gauge pressure). The caveat is that this is still happening before or at the inlet connection. Some examples include:
- Loose Tri-Clamp connections.
- Improperly seated gaskets.
- Cracked suction hoses.
- Poor suction conditions.
- Vortexing at the supply tank.
- Improperly purged hoses or vessels (especially during dry hopping).
- Products that naturally contain entrained air (such as yogurt, peanut butter, whipped products, or some oils).
When air becomes trapped in your pump, it can lead to numerous operational issues. You will notice symptoms such as noisy operation, excessive vibration, loss of prime, and overall decreased performance. If left unresolved, air entrainment can cause reduced flow, increased wear, and may contribute to conditions that lead to cavitation.