An air knife that is not very strong is not always too small. The problem is often where the air gets into the air knife. For blades one place where the air comes in may be enough to fill the space inside the air knife. For longer blades the air has to travel a longer distance inside the air knife before it comes out. If the air comes in at the place one side of the air knife might hit really hard while the other side might leave water behind.
This is why it matters whether you choose an air knife with one place for the air to come in or two. Where the air comes in affects how the air is spread out how evenly things get dry how well the fan works with the air knife how much air is lost in the duct. How easy it is to put the system on the machine. It is not a thing to decide on. It is a part of how the air is delivered.
For people who buy these things and the engineers who design them the main question is an one: can one place where the air comes in provide a strong blast of air all along the length or do you need two places for the air to come in to keep the air flowing evenly from one end, to the other of the air knife?
An air knife is a pressurized chamber with a narrow slot or hole pattern. Air enters the body through one or more inlets, fills the internal plenum, and exits as a controlled sheet of air. The product only sees the final air curtain, but the curtain depends on what happens inside the knife body first.
If internal pressure stays stable, the air exits the slot at nearly the same force across the working length. If the pressure drops toward the far end, the air curtain becomes uneven. On a drying line, the weak zone becomes the limit. Operators may raise blower pressure to fix the wet side, but that can over-blow the strong side, increase noise, move light products, or waste power.
A good inlet configuration reduces that problem. It helps the air reach the full plenum without asking one end of the knife to do too much work.
A dual-inlet air knife has two air connections, usually arranged so the plenum receives air from both sides or from two balanced feed points. The goal is not simply to add more air. The goal is to make the air supply more even across the length.
QXY Machinery's standard reference is direct: aluminum air knives up to 600 mm commonly use one inlet, while knives over 600 mm move to dual inlets to help maintain balanced airflow. The same logic applies in many wide conveyor, sheet, panel, PCB, bottle, and glass drying applications.
On a long knife, dual inlets reduce the distance air must travel inside the body. That can improve pressure balance, reduce weak-end drying, and make blower selection more predictable. It also helps when the line needs a wider slot gap or higher total flow because the air demand is shared by two feed points.
Selection point | Single-inlet air knife | Dual-inlet air knife |
Typical length | Short to medium knives; often <=600 mm in QXY aluminum references. | Longer knives; commonly >600 mm in QXY aluminum references. |
Airflow balance | Works well when length and slot demand are modest. | Helps pressure stay stable across long blades. |
Installation | Simple piping and fewer hose connections. | Needs balanced duct routing and room for two connections. |
Best fit | Narrow conveyors, small parts, localized blow-off. | Wide conveyors, panels, sheets, PCB lines, heavy liquid load. |
Main risk | Weak far-end airflow if the knife is too long. | Uneven supply if one duct branch has more restriction. |
Two inlets do not automatically solve every drying problem. If one duct branch is shorter, cleaner, or less restricted than the other, the two sides may not receive the same air volume. The result can look very similar to a single-inlet imbalance: one side dries well and the other side stays wet.
A balanced Y-split manifold is usually better than a casual tee with one short branch and one long branch. Hose diameter, bend radius, filter condition, clamps, leakage, and branch length all matter. On wider lines, the duct layout should be reviewed with the air knife, not added after the knife is already selected.
Maintenance teams should also check both branches over time. A partially blocked filter, loose clamp, crushed hose, or dirty inlet screen can make a dual-inlet system drift out of balance after installation.
The easiest symptom is a wet stripe or wet edge at the far end of the blade. If drying is strong near the inlet and weak away from it, inlet distribution should be checked before replacing the air knife or increasing blower size.
Another symptom is unstable adjustment. Operators raise pressure to fix one side, then the opposite side splashes water, shakes product, or creates too much noise. That usually means the system is compensating for a weak zone instead of fixing the pressure balance.
A third symptom is repeated complaints after maintenance. If the system works after setup but gradually becomes uneven, inspect the duct branches, filters, inlet connections, slot condition, and bracket alignment. Inlet balance and installation condition work together.
When you have a blade and the area you need to dry is not very wide a single-inlet air knife is a good option. This is also the case when you do not have a lot of liquid to deal with and you want the pipes to be simple. It is great for machines, tiny parts and narrow conveyor belts when you just need to blow air on a small spot.
You should use a dual-inlet air knife when your blade is long and the area you need to dry is wide. This is also a choice when you need to make sure everything is evenly dry from one end to the other. If you only have one inlet it might not be able to handle a space. Dual-inlet air knives are usually the choice, for big machines that deal with long panels cleaning electronic parts making glass drying metal strips working with textiles and drying rows of bottles or containers that need a lot of air.
Before final selection, prepare the product width, air knife length, slot width, air source type, available blower, duct route, machine drawing, working distance, line speed, liquid type, material requirement, and maintenance access. These details let QXY Machinery recommend an inlet layout that fits the real machine instead of only the catalog dimension.
Parameter | QXY reference value |
Standard aluminum lengths | 150, 300, 450, 600, 800, and 1000 mm |
Custom length | Up to 6,000 mm for special line widths |
Inlet threshold | 1 inlet for <=600 mm knives; 2 inlets for >600 mm knives |
Standard inlet diameter | 50 mm standard; multiple sizes available by model |
Slot gap | 0.5-2 mm standard for general industrial drying |
Airflow uniformity | +/-5% factory calibration target across knife length |
Working pressure | 2-6 psi (0.14-0.42 bar) for blower-driven systems |
Working distance | 20-50 mm for many drying applications |
These values are useful starting points. Final configuration still depends on the process. A 900 mm air knife on a slow, light-duty line may not have the same demand as a 900 mm knife removing heavy rinse water at high speed. The inlet layout, blower, ducting, and bracket position should be selected as one system.
QXY Machinery (Shenzhen Qixingyuan Machinery Equipment Co., Ltd.) is a high-tech enterprise integrating R&D, design, production, and sales, specializing in drying, dust removal, and water-blowing solutions for industrial applications. With over 10 years of focused expertise in the air knife field, QXY Machinery has developed a mature technical foundation and a complete in-house R&D system.
QXY Machinery produces over 15 standard air knife types, including aluminum alloy, stainless steel, PVC, titanium alloy, small hole PCB knives, ring air knives, tornado air knives, and air-to-air configurations. For inlet-sensitive applications, QXY can support custom air knife length, custom slot width, custom inlet configuration, and blower matching based on the drying area and machine layout.
QXY Machinery operates a complete production system supported by ample raw material supply and strict quality management. Stable processing capabilities and professional technical expertise enable reliable products, precise application support, and efficient after-sales service.
Q: What is the main difference between a single-inlet and dual-inlet air knife?
A: A single-inlet air knife has one air connection feeding the plenum. A dual-inlet air knife has two air connections so long blades can receive air more evenly from both sides or from two feed points.
Q: When should I choose a dual-inlet air knife?
A: Choose dual inlet when the knife is long, the drying width is wide, the line needs stable edge-to-edge drying, or a single inlet would leave a weak far-end zone. QXY commonly uses dual inlets for standard aluminum knives longer than 600 mm.
Q: Is a dual-inlet air knife always stronger?
A: Not automatically. Dual inlets help distribute air, but the blower and duct branches still need enough capacity and balance. Poor piping can make a dual-inlet system uneven.
Q: Can I use one blower for a dual-inlet air knife?
A: Yes. Many dual-inlet systems use one blower with a balanced Y-split manifold. The important point is that both branches should have suitable diameter, similar resistance, tight connections, and enough flow after the split.
Q: Why is one side of my air knife weaker than the other?
A: Possible causes include an air knife that is too long for one inlet, an unbalanced dual-inlet manifold, duct leakage, blocked filters, a dirty slot, or bracket misalignment that changes the working distance.
Q: Does inlet configuration affect energy use?
A: Yes. If the inlet layout is wrong, operators may raise blower pressure to compensate for weak zones. A balanced inlet configuration can reduce this kind of waste, but it must be matched with the right blower and ducting.
Q: What information should I send before choosing single inlet or dual inlet?
A: Send the required knife length, product width, line speed, drying target, liquid load, slot gap if known, available air source, duct route, machine drawing, material requirement, and photos of the installation space.
Shenzhen Qixingyuan Machinery Equipment Co., LTD.
info@airknifecn.com
Building 8, Wanfeng Third Industrial Zone, Xinqiao Street, Bao'an District, Shenzhen, Guangdong, China
