What exactly is a seal-air fan, and why does the pressure have to be held so precisely?
A seal-air fan pressurises the air path across a shaft or labyrinth seal so that hot or dirty process gas cannot track back along the shaft and into the bearing or the surrounding area. The seal-air supply has to stay above the process-side pressure at all times, typically 50 to 300 mmWC above it, because the moment it falls below, the seal reverses and process gas leaks past. That is why the design is driven by pressure margin, curve stability and reliability rather than by flow: the fan is a protection device, and the pressure it holds is the protection.
Why is high static hard to get from a small fan?
Pressure rise comes from tip speed, so a compact wheel asked for high static has to spin faster, and higher tip speed on a small rotor raises bearing loads, shaft stress and noise together. We handle it by choosing the right wheel for the pressure ratio, a high-static backward-curved or backward-inclined wheel where efficiency still matters and a radial or radial-tipped wheel where the ratio is extreme and robustness matters more, then sizing the shaft, tip speed and bearings to the pressure rise rather than to the flow. Bearing life is held to a design target of L10h greater than or equal to 40,000 hours.
These fans run at low flow and high pressure. How do you stop them hunting or stalling?
Low flow at high pressure is the region where a fan curve flattens and can droop, and a fan sized onto that part of the curve hunts and oscillates, so the pressure it is meant to hold steady starts to swing. We engineer the duty point onto the falling, stable portion of the selected wheel, typically 5 to 15 percent to the right of the peak and well clear of the droop, so the pressure holds steady across the operating band. We then verify the curve on the 200 HP VFD test rig before dispatch, so the stability is proven and not assumed.
This fan protects a critical machine. How do you build for availability?
We treat seal air, bearing cooling and critical boost as protection duties, because if the fan stops the seal leaks, the bearing overheats, or the process trips. So the build is an availability build: bearing life to a design target of L10h greater than or equal to 40,000 hours continuous, generous motor and drive margin, and a duty and standby (2x100 percent) or N+1 configuration where a stop cannot be tolerated. We add pressure and temperature instrumentation so that a healthy, proven-running fan releases the machine it protects, rather than the machine running on an assumption.
Should I specify VFD or a damper for control?
VFD is our default. Seal and cooling set-points shift with the load on the machine being served, and a drive holds the target pressure or cooling flow across the range while avoiding the throttling loss of a damper at part-load. A discharge or inlet damper remains available where the set-point is genuinely fixed and a drive is not warranted, or on a legacy retrofit where the existing motor and starter cannot take a drive. We quote whichever your installation calls for.
Can the fan sit in a classified (ATEX) area around rotating equipment?
Yes. Where the seal-air, cooling or booster fan sits in a classified area, for example around rotating equipment in oil and gas or chemicals, we build spark-resistant construction and self-declare ATEX Zone 2/22 per 2014/34/EU, Category 3, with a non-sparking or aluminium impeller, bonded earthing and T-class bearing-temperature control. To be precise, that is a self-declaration of conformity, not a third-party certification. We mark the area classification and the build on the GA drawing and nameplate.
What is the lead time for a seal / cooling / booster fan?
A standard engineered unit runs roughly 8 to 13 weeks order-to-dispatch: offer in 3 to 5 working days, GA drawing 2 to 3 weeks from PO, manufacture, balance and paint 5 to 9 weeks, and performance test plus FAT about a week. A duty and standby package, an ATEX self-declared build, or a high-static compact wheel with tighter balancing adds file preparation and runs a little longer. These are small fans with large consequences, so we engineer to your seal or cooling duty rather than offer a nearest catalogue frame; specify yours and we confirm a dated commitment against it, not a placeholder.
What standards and certifications actually apply to these fans?
Performance is tested in-house to the AMCA 210 / ISO 5801 method on our 200 HP VFD test rig; that is testing to the method, not an AMCA certification, and we are not an AMCA member. Balancing is to ISO 21940, G6.3 as standard and G2.5 or G1.0 on application, and bearing life is a design target of L10h greater than or equal to 40,000 hours. CE is self-declared per 2006/42/EC and 2014/35/EU, and ATEX Zone 2/22 is self-declared per 2014/34/EU (Category 3) where the area classification calls for it; to be precise, those are self-declarations of conformity, not third-party certifications. Our only third-party certification is ISO 9001:2015.
