In commercial plant rooms, a small plate heat exchanger pressure drop is normal, however, a sudden or gradual increase in differential pressure (∆P) across a plate heat exchanger signals compromised system health.
The Problem: When differential pressure exceeds design limits, circulating pumps are forced to overwork to overcome resistance, heat transfer rates drop significantly due to restricted fluid flow and mechanical wear on gaskets and system components accelerates.
What Causes Excessive Pressure Drop in a Plate Heat Exchanger?
- Mineral Scaling & Chemical Fouling
- Particulate Debris & Biofouling
- Incorrect Plate Compression
- Excessive Fluid Flow Rates
- Gasket Swelling & Port Distortion
1. Mineral Scaling & Chemical Fouling
In domestic hot water (DHW) and high-temperature systems, mineral build-up (mostly calcium carbonate (CaCO₃)) is the leading cause of flow restrictions. This is because, as water is heated, these minerals form a hard layer of scale on the stainless-steel plates.
- The Impact: A scale layer of just 0.5mm can reduce heat transfer efficiency by 30% and narrow the plate channels, increasing flow resistance.
- How to Fix: Perform a chemical Clean-In-Place (CIP) flush using an acidic descaling agent. For severe scaling, dismantle the plate heat exchanger and clean each plate with a soft nylon brush.
2. Particulate Debris & Biofouling
Bypassed strainers or missing secondary filters allow pipe scale, rust, weld slag, dirt and biological sludge to settle directly at the plate pack inlet ports, creating immediate blockages.
- The Impact: Debris build-up can block the narrow plate channels, increase pressure drop, reduce heat transfer and, in severe cases, cause complete flow blockage.
- The Fix: Install a minimum 40-mesh Y-strainer or basket filter upstream on all ports and clean it regularly. Where fitted, use back-flushing valves to reverse the flow and flush trapped debris safely to a drain.
3. Incorrect Plate Compression
After maintenance, a plate heat exchanger (PHE) must be reassembled with the correct plate compression. Tightening the plate pack too much or too little changes the spacing between the plates, affecting flow, pressure and sealing.
The plate pack should always be tightened to the manufacturer’s specified ‘A’ dimension (the distance between the frame plates).
| Plate Condition | ‘A’ Dimension | Impact |
| Over-tightened | Below minimum limit | Narrows the flow channels, increases pressure drop (ΔP) and can damage the plates or gaskets. |
| Under-tightened | Above maximum limit | Can cause internal bypass, external leaks and reduced flow velocity. |
- How to Fix: Always tighten the PHE to the manufacturer’s specified ‘A’ dimension (shown on the data plate or in the manual). Use a calibrated torque wrench and tighten the bolts evenly, checking the measurement at all four corners throughout the process.
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4. Excessive Fluid Flow Rates
A PHE is designed to operate with a specific flow rate. If the flow rate is too high, often due to upgraded pumps, incorrectly configured variable speed drives or balancing valves being left fully open, it can significantly increase pressure drops across the PHE.
- The Impact: Pressure drop increases much faster than flow rate. As a rule of thumb, doubling the flow rate can increase the pressure drop by around four times (400%), reducing system efficiency and placing extra stress on the heat exchanger.
- How to Fix: Measure the system flow rate using an ultrasonic flow meter or installed flow gauges. If the flow exceeds the design specification, adjust the variable speed drive (VSD) or balancing valves to restore the correct flow rate.
5. Gasket Swelling & Port Distortion
Incorrect glycol concentrations, aggressive water treatment chemical or operating temperatures above the gasket’s rated limit can cause EPDM or NBR gaskets to soften, swell or deform. This can restrict flow, cause leaks and reduce PHE performance.
- Impact: Damaged gaskets can obstruct the flow channels, increase pressure drop, reduce heat transfer efficiency and cause leaks.
- How to Fix: Inspect gaskets during routine maintenance for signs of swelling, softening, cracking or distortion. Replace any damaged gaskets with OEM-approved spare parts.
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