Danfoss High-Pressure Pumps for Desalination: APP & PAH Series Guide 2026
Posted by ForeverPure Engineering Team on Apr 9th 2026
Updated April 2026
Danfoss high-pressure pumps are the gold standard for seawater reverse osmosis (SWRO) desalination systems worldwide. Their axial piston design delivers the extreme pressures required for seawater desalination (800–1,000 PSI) with industry-leading energy efficiency. This guide covers the APP and PAH series to help engineers specify the right pump for their desalination project.
Why Danfoss for Desalination?
Danfoss dominates the SWRO pump market because their axial piston technology offers critical advantages over triplex plunger pumps at high pressures:
- Highest volumetric efficiency — 95%+ at operating pressure, reducing energy consumption per cubic meter of permeate
- Compact footprint — 40–60% smaller and lighter than equivalent triplex pumps, critical for containerized systems
- Smooth flow delivery — Minimal pulsation reduces stress on membranes, piping, and instruments
- Low maintenance — Fewer wearing parts than triplex pumps; 8,000+ hour service intervals
- Variable speed compatible — Pair with VFD for precise pressure control and energy optimization
Danfoss APP Series (Axial Piston Pumps)
The APP series is designed specifically for SWRO desalination, delivering pressures up to 80 bar (1,160 PSI) at flow rates matching the most common membrane configurations.
| Model | Flow Rate | Max Pressure | Motor Power | Typical SWRO Capacity |
|---|---|---|---|---|
| APP 0.6 | 0.6 m3/h | 80 bar | 2.2 kW | 500–1,000 GPD |
| APP 1.0 | 1.0 m3/h | 80 bar | 3 kW | 1,000–3,000 GPD |
| APP 1.5 | 1.5 m3/h | 80 bar | 4 kW | 3,000–5,000 GPD |
| APP 2.5 | 2.5 m3/h | 80 bar | 5.5 kW | 5,000–10,000 GPD |
| APP 3.5 | 3.5 m3/h | 80 bar | 7.5 kW | 10,000–15,000 GPD |
| APP 5.1 | 5.1 m3/h | 80 bar | 11 kW | 15,000–30,000 GPD |
| APP 10.2 | 10.2 m3/h | 80 bar | 22 kW | 30,000–80,000 GPD |
| APP 21 | 21 m3/h | 80 bar | 45 kW | 80,000–200,000 GPD |
| APP 36 | 36 m3/h | 80 bar | 75 kW | 200,000–500,000 GPD |
Danfoss PAH Series (High-Flow Piston Pumps)
The PAH series serves large-scale desalination plants requiring higher flow rates. These heavy-duty triplex piston pumps deliver flows up to 60 m3/h at pressures up to 80 bar.
PAH pumps are typically used in systems above 200,000 GPD where a single high-flow pump is more practical and economical than multiple APP units in parallel.
Energy Efficiency: Why It Matters
In a typical SWRO system, the high-pressure pump consumes 60–70% of total system energy. Danfoss APP pumps achieve specific energy consumption as low as 2.5 kWh/m3 when paired with energy recovery devices — approaching the thermodynamic minimum for seawater desalination.
Pairing a Danfoss APP with a ERI PX pressure exchanger or FEDCO LPS turbocharger reduces pump motor size by 40–60%, cutting both capital cost and lifetime energy expenses.
Sizing a Danfoss Pump for Your SWRO System
To select the correct APP model:
- Determine feed flow rate — This is the total flow to the membrane array (permeate + concentrate). For 40% recovery: feed flow = permeate flow ÷ 0.40.
- Select operating pressure — Typically 55–70 bar for SWRO. Higher TDS or lower temperature requires higher pressure.
- Account for energy recovery — If using an ERD, the APP only needs to pump the permeate portion of total flow at full pressure; the ERD handles the rest.
- Choose motor voltage — 400V/50Hz or 460V/60Hz, depending on location. VFD recommended for all installations.
Maintenance Schedule
- Every 2,000 hours: Check shaft seal for leakage, inspect suction strainer
- Every 4,000 hours: Replace shaft seal, check valve plate clearance
- Every 8,000 hours: Major overhaul — replace pistons, cylinder block, valve plate, and all seals
- Ongoing: Monitor suction pressure (minimum 1.5 bar), discharge pressure, motor current, and vibration
Browse all Danfoss pumps at ForeverPure →
Frequently Asked Questions
What is the difference between Danfoss APP and PAH pumps?
APP (Axial Piston Pump) is a compact, high-efficiency design for small to large SWRO systems up to 36 m3/h. PAH is a heavy-duty triplex piston pump for very large plants requiring flows up to 60 m3/h. For most commercial and industrial desalination systems, APP is the standard choice.
Can I use a Danfoss pump without energy recovery?
Yes, but it is not recommended for systems above 5,000 GPD. Without energy recovery, the pump must pressurize all feed water to operating pressure, increasing motor size and energy consumption by 40–60%. Energy recovery devices pay for themselves within 1–2 years through electricity savings.
Does ForeverPure stock Danfoss pump parts?
Yes. ForeverPure stocks common Danfoss APP spare parts including shaft seals, valve plates, piston assemblies, and seal kits. We can also source any Danfoss part through our authorized distributor relationship. Contact us with your pump model number for parts availability and pricing.
Need a Danfoss pump for your desalination project? Request a quote → or call +1-408-969-2688.