The pressure a blower makes at its flange is not the pressure your process gets. Every metre of pipe, every bend, valve and fitting between the blower and the point of use eats a slice of it. Undersize the pipework and you can lose so much pressure to friction that a correctly-sized blower still fails to do the job. Good piping design keeps velocity sensible and losses low, so the blower's rated pressure reaches the work. This guide gives the rules.
It follows directly from installation best practices and is the first thing to check when a system reads low pressure.
Why pressure disappears in pipework
Two mechanisms:
- Friction loss along straight pipe — rises with the square of velocity and with length, and falls hard as diameter grows.
- Fitting loss at bends, tees, valves, reducers and the diffuser/nozzle itself — each adds an equivalent length of straight pipe.
Because friction scales with velocity squared, the pipe diameter is the dominant lever. Slightly larger pipe drops velocity, and velocity-squared means the loss falls dramatically. Undersized pipe is the classic false economy: cheaper to buy, expensive forever in wasted pressure and energy.
Keep velocity in the right band
The design target for blower air is a header velocity of roughly 15-20 m/s. Too high and friction loss soars; too low and the pipe is needlessly large and costly (and in conveying duty, too-low velocity lets material drop out).
Velocity is flow divided by pipe cross-section:
velocity (m/s) = flow (m³/s) ÷ area (m²)
Work the flow in m³/s. If your blower is rated in m³/hr, divide by 3600; if in CFM, convert first with the CFM to m³/hr guide (×1.699), then divide by 3600.
Worked example
A YEBL-1-400 delivers 400 m³/hr = 0.111 m³/s.
- Through 50 mm bore (area 0.00196 m²): velocity = 0.111 ÷ 0.00196 = 56.6 m/s — far too fast, huge friction loss.
- Through 80 mm bore (area 0.00503 m²): velocity = 0.111 ÷ 0.00503 = 22.1 m/s — close, slightly high.
- Through 100 mm bore (area 0.00785 m²): velocity = 0.111 ÷ 0.00785 = 14.1 m/s — comfortable.
So for 400 m³/hr, 80-100 mm header pipe is right; 50 mm would throttle the blower badly. This is exactly how an oversized blower ends up "underperforming" — the pipe, not the machine, is the bottleneck.
| Flow (m³/hr) | Flow (m³/s) | For ~15-20 m/s, use bore |
|---|---|---|
| 145 | 0.040 | 50-65 mm |
| 210 | 0.058 | 65-80 mm |
| 400 | 0.111 | 80-100 mm |
| 700 | 0.194 | 100-125 mm |
| 1050 | 0.292 | 125-150 mm |
Fittings cost pressure too
Each fitting behaves like a length of extra straight pipe. Rough equivalent lengths (as multiples of pipe diameter, D):
| Fitting | Approx equivalent length |
|---|---|
| 90° sharp elbow | ~30 D |
| 90° long-radius bend | ~20 D |
| 45° bend | ~16 D |
| Tee (through flow) | ~20 D |
| Tee (branch flow) | ~60 D |
| Gate valve (open) | ~8 D |
The lesson: minimise bends, use long-radius sweeps instead of sharp elbows, and avoid unnecessary tees and valves. A tangled pipe run with six sharp elbows can add tens of metres of equivalent length, quietly consuming pressure the blower needed for the process.
Design rules that keep losses low
- Size for velocity first, then confirm the total loss is a small fraction of the blower's rated pressure.
- Short and straight beats long and bendy. Route the pipe the direct way.
- Long-radius bends, not sharp elbows.
- Match the diffuser/nozzle to the flow — the end device is often the biggest single loss; do not starve it with undersized feed pipe.
- Add up the losses — straight-pipe friction + all fitting equivalents + the end-device loss — and check the blower's rated pressure exceeds the sum with margin.
- Support the pipe independently so its weight never bears on the blower (see installation).
- Watch the energy cost. Every mbar wasted in the pipe is energy paid for and thrown away — check it with the /tools/energy-savings-calculator.
Include the losses when you size the blower
Here is how the pieces fit. You do not size a blower to the process pressure alone — you size it to process pressure + system losses:
Required blower pressure = pressure at point of use + pipe friction + fitting losses + filter/silencer loss
Get this sum wrong (typically by ignoring the losses) and a blower that looks right on paper falls short in the field. When you send us a duty, tell us the pipe run — length, bore, number of bends, and the end device — and we will factor the losses into the model selection so the rated pressure actually reaches the work. For high-loss systems, a high-pressure series machine may be the honest answer.
Material and layout choices that reduce loss
Beyond diameter and bend count, a few layout decisions quietly protect your pressure:
- Smooth-bore pipe loses less than rough or corroded pipe. An old, scaled internal surface raises friction over time — a reason blower systems can lose pressure years into service with no fault in the machine.
- Gradual reducers, not sudden steps. Where pipe size changes, a tapered reducer loses far less than an abrupt shoulder.
- Full-bore valves (like a full-bore ball or gate valve) barely restrict flow when open; globe and angle valves cost much more. Choose the valve type for low loss, not just for shut-off.
- Balance branches. In a manifold feeding several diffusers, unequal branch lengths deliver unequal flow. Balance the layout, or fit balancing at each drop, so every diffuser gets its share.
| Choice | Lower loss | Higher loss |
|---|---|---|
| Bend | Long-radius sweep | Sharp elbow |
| Size change | Tapered reducer | Sudden step |
| Valve (open) | Full-bore ball/gate | Globe/angle |
| Internal surface | Smooth, new | Rough, scaled |
Recheck the system as it ages
Pipe losses are not fixed for life. Over years, scale builds inside pipe, diffusers foul, and filters are sometimes swapped for the wrong size — all of which raise the system resistance the blower must overcome. A blower that met its duty at commissioning can slowly fall behind not because the machine weakened but because the system got harder to push through.
This is why an unexplained gradual pressure shortfall should send you to the low-pressure troubleshooting guide to check the system, not just the blower. Re-measure the actual delivered pressure at the process periodically and compare it to the blower's gauge pressure: a widening gap between the two is the pipe and end-devices loading up, and it is costing energy every hour — quantify it with the /tools/energy-savings-calculator. Cleaning a fouled diffuser or descaling a header can restore performance without touching the blower at all.
Send us the layout
A sketch of the pipe run and the duty point is all we need. Our engineers will estimate the system loss and put the right Yash blower against it — with pressure to spare where the pipe cannot be helped.
- WhatsApp: +91 9311693322
- Email: sales@yashblowers.org
Yash Blowers, Faridabad, since 1998. The blower makes the pressure; the pipe decides how much survives.