If you’re a plumber or someone who works with pumps, you’ve probably heard about NPSH (Net Positive Suction Head). But what is it exactly, and how do you calculate it? Let’s break it down step-by-step in simple terms.

---

🔎 What Is NPSH?

NPSH is about ensuring there’s enough pressure in your system to get liquid into the pump without it turning into vapor (causing bubbles).

There are two key parts:

1. NPSHa (Available): The pressure your system provides to the pump.

2. NPSHr (Required): The minimum pressure the pump needs to work without issues.

For your pump to work correctly:

NPSHa must be greater than NPSHr.

---

📏 How Do You Calculate NPSHa?

You can calculate the Net Positive Suction Head Available using this formula:

NPSHa = Hs + Ha - Hv - Hf

Here’s what each term means:

Hs: Static head (the vertical height of the liquid above the pump).

Ha: Atmospheric pressure (depends on your elevation).

Hv: Vapor pressure (depends on the liquid temperature).

Hf: Friction losses in the suction piping (caused by flow resistance).

---

🔧 Step-by-Step Guide to Working It Out:

1. Measure Static Head (Hs):

If the liquid source is above the pump, measure the height in meters or feet.

If below the pump, this will be negative.

2. Find Atmospheric Pressure (Ha):

At sea level, atmospheric pressure is 101.3 kPa or 10.3 meters of water.

Adjust for your elevation (e.g., in Toowoomba, QLD, it’s about 9.5 meters).

3. Determine Vapor Pressure (Hv):

Look up the vapor pressure of your liquid at its operating temperature (this info is usually in data sheets).

4. Calculate Friction Loss (Hf):

Use pipe size, length, and fittings to calculate pressure losses in the suction line. (Use online calculators or friction loss charts to make this easier.)

5. Plug the Numbers Into the Formula:

Add Hs and Ha, subtract Hv and Hf, and you’ll have your NPSHa.

---

⚠️ What’s Next?

Compare your NPSHa to the pump’s NPSHr (found in the pump datasheet). If NPSHa > NPSHr, you’re good to go. If not, you’ll need to:

Lower the pump’s suction height.

Use larger suction pipes to reduce friction losses.

Reduce liquid temperature to lower vapor pressure.

---

💡 Let Us Help You!

If this still sounds a bit overwhelming, don’t stress. At Quality Pumps, we can help you calculate NPSH, choose the right pump, and design your system to avoid issues like cavitation.

🔄 Share this post with your mates in the t

rade—it might just save their pump!

#QualityPumps #NPSHExplained #PumpEfficiency #PumpDesignTips