You can’t make diamonds without pressure, and a pneumatic conveying system won’t work without pressurized air. Rotary airlock valves need to maintain a specific pressure differential — that’s the “airlock” part — to move your material at a specific rate.
When airflow isn’t optimized, the valve’s rotor pockets can fill with too much air, which can hamper material flow and reduce its fill capacity. To combat this issue, rotary airlock valves can be equipped with a housing vent port.
In short, removing excess air prevents issues and improves the valve’s fill capacity, so you can move more material in the same amount of time. Keep reading to learn how it works.
What is a housing vent port?
A housing vent port is an opening drilled into the return side of the valve’s housing to vent blow-by air and relieve pressure. The port connects to a vent line that directs the released air to another part of the system. Vent ports are highly recommended for applications prone to airflow issues.
Rotary valves equipped with a vent port generally benefit from better fill capacity, smoother material flow, and a longer lifecycle.
Which industries need vent ports?
If your application requires a pneumatic conveying system with pressures exceeding 6 PSI and you handle pellets, granules, or powders, you likely need a housing vent port. Common materials include plastic pellets, sand, and flour.
Other industries can also benefit from more controlled airflow, so a vent port may be recommended as an optional feature to boost efficiency.
What problems are caused by blow-by air?
Let’s start with some basics. Material enters at the valve’s inlet, filling the rotor pockets as they move down to the outlet — this is called the load side of rotation. At the outlet, material is released into the next vessel, and the empty vanes come back up to the return side to catch more material.
The pneumatic conveying line sits below the valve, and blow-by air can sometimes leak into the valve’s return side from the outlet. As rotation continues, pressurized air builds up in the rotor pockets, taking up space that’s meant for your ingredients. That means the valve will keep spinning at the same rate as usual, but you’ll be moving less material.
When larger amounts of air come up the return side, you can start to see pulsing in the flow of material, which can cause other issues in the conveying line. Excess air can also cause abrasion inside the valve by “sandblasting” material against its internal surfaces.
How do vent ports solve the issue?
We use housing vent ports to maintain an efficient pocket fill capacity and prevent flow issues. Any excess air that comes up the return side gets released through the port, then travels through the vent line to a dust collector, cyclone, silo, or hopper.
It’s a simple and effective system for relieving excess air before it has a chance to interfere with material flow, abrade your valve parts, or slow down performance.
Keep in mind that a minimal amount of material can fail to discharge from the airlock and get pulled into the vent line. This is normal, and the common practice is to have a negative draw on the vent line — about 2–3 W.C., depending on the application — to pull the released air and product to its destination.
If you ever see excessive amounts of material entering the vent line, shut down the system and investigate. It could indicate a problem with the conveying system, such as a plugged line blower failure, an overloaded blow-through adapter, or an undersized blower.
What does your valve need?
If you’re not sure whether your rotary airlock can benefit from a housing vent port, speak with the conveying experts at ACS Valves. We’ll only recommend what you need to get the best performance and ROI for your application — no fancy extras. Just give us a call.
