At a glance
- Type
- Oil-lubricated screw
- Architecture
- Two-stage
- Pressure options
- 8 / 10 / 13 bar
- Selection
- By FAD and pressure
Overview
DUALLUBE is an oil-lubricated two-stage screw air compressor that splits the compression process across two separate sets of helical rotors. Dividing the total compression ratio into two steps lowers internal leakage, reduces bearing stress, and can deliver up to 15% more airflow using the same power as a single-stage unit. It is for plants that need a two-stage machine rather than a single-stage SILVERLUBE unit.
Model range
DUALLUBE is the two-stage oil-lubricated family. Pressure options are 8, 10 and 13 bar.
Architecture
Two-stage screw
- Pressure options
- 8 / 10 / 13 bar
- Why two-stage
- Higher pressure ratio and up to 15% more airflow
- Not the same as
- SILVERLUBE single-stage
How to choose
By duty point
- Start with
- Required FAD and pressure
- Then check
- Whether two-stage is needed
- Before a quote
- Confirm the model row
Technology
Technology Platform
DUALLUBE D uses two-stage compression with oil-injected twin-screw technology. Air is compressed to intermediate pressure in the first-stage screw element, then passes through an intercooler where its temperature is reduced before entering the second-stage screw element for compression to final pressure.
Performance Boundaries
Compared with single-stage compression (SILVERLUBE S), two-stage compression shows a significant advantage under the following conditions:
Key Design Decision: Why Standard VFD (VPM)?
Why does DUALLUBE D have variable-frequency drive (VPM) as standard across the entire range?
More technical detail
Technology Platform
From a thermodynamic perspective: isothermal compression is the theoretically most efficient compression process. Single-stage compression deviates further from the isothermal ideal because of its larger temperature rise. Two-stage compression reduces the per-stage temperature rise through intercooling, bringing the overall process closer to isothermal compression and thereby lowering input power per unit of airflow.
Performance Boundaries
Industry knowledge: at rated conditions, two-stage compression reduces specific power by 5–15% compared with single-stage compression. The actual figure depends on the specific pressure ratio, model and operating conditions. This range represents category knowledge, not a SIND commitment for a specific model.
- Power ≥ 45 kW — at smaller power ratings, the energy-efficiency gain from two-stage compression does not offset the higher purchase cost.
- Pressure ≥ 8 bar(g) — the higher the pressure ratio, the greater the benefit of intercooling.
- Low-pressure range 4–5 bar(g) — although the pressure ratio is lower, two-stage machines still offer an efficiency advantage in high-flow low-pressure applications. The VPM-B series covers 22–280 kW in this range.
- Continuous operation with stable load — the return on investment for two-stage machines is realised fastest in high annual operating-hour scenarios.
Key Design Decision: Why Standard VFD (VPM)?
Two-stage compressors carry a higher purchase cost than single-stage machines of equivalent power. Running at fixed speed would introduce unload-cycle losses at partial load, undermining the efficiency advantage. Standard VPM ensures that two-stage machines deliver their efficiency benefit across all load conditions — variable-frequency control matches air output to air demand, eliminating unload losses and realising the thermodynamic advantage of two-stage compression across the full operating range.
The low-pressure variant (VPM-B suffix) follows the same design philosophy: intercooling plus variable-frequency drive, covering high-flow 4–5 bar(g) applications.
Selection Logic
DUALLUBE D selection is based on two parameters: required pressure and required flow. The following constraints apply:
Selection advice: if a factory has both 8 bar and 4 bar air requirements, do not select a single two-stage machine and step the pressure down to 4 bar for all outlets. Instead, use separate pressure supplies — a high-pressure machine for high-pressure needs and a low-pressure machine for low-pressure needs — to avoid degrading high-grade energy.
- Standard pressure range (8 / 10 / 13 bar) starts at 45 kW. For standard-pressure requirements below 45 kW, use SILVERLUBE S.
- Low-pressure range (4 / 5 bar) starts at 22 kW with the VPM-B suffix. The 22, 30 and 37 kW ratings exist only in the low-pressure range and do not appear in the standard-pressure range.
- 200 kW appears in both the standard-pressure and low-pressure families within DUALLUBE D.
Selection & quote checklist
- the exact DUALLUBE two-stage model
- required operating pressure
- free air delivery at that pressure
- electrical supply
- why two-stage is required
- the current datasheet and package contents
Applications
Scenario A: Large manufacturing plant — whole-site air supply
An automotive-parts factory with CNC machining centres, pneumatic clamps and spray lines drawing air simultaneously.
Scenario B: Low-pressure pneumatic conveying
A cement plant’s pneumatic conveying system for powdered materials requires 80–120 m³/min at 4 bar(g) — high flow, low pressure. Selection: DUALLUBE D 160A-4VPM-B or D 200A-4VPM-B.
Scenario C: Replacing multiple small machines
A factory currently operates three 37 kW fixed-speed single-stage machines in parallel, totalling 111 kW installed power at an average load of about 60%.
More application detail
Industry Matrix
| Industry | Typical pressure bar(g) | Typical power kW | Notes |
|---|---|---|---|
| Steel | 8–13 | 90–280 | Continuous-casting pneumatic equipment; continuous operation |
| Chemical | 8–13 | 75–280 | Reactor pressurisation, material conveying; high-flow continuous duty |
| Cement / Building materials | 4–8 | 75–280 | Powder conveying, kiln-head atomisation; low-pressure high-flow |
| Textile | 6–8 | 45–160 | Air-jet looms; requires stable pressure, pulse-free delivery |
| Electronics | 8–10 | 45–160 | Cleanroom base-load air supply (requires downstream oil-removal treatment) |
| Food / Beverage | 4–8 | 45–160 | Bottle blowing, filling, packaging (requires downstream oil-removal treatment) |
Installation Considerations
- Intercooler heat dissipation — the intercooler adds to the total heat load of the machine. Compressor-room ventilation design must account for this additional heat output.
- Footprint — two-stage machines are larger than single-stage units of the same power rating because of the additional intercooling circuit. Confirm dimensions during selection.
- Maintenance access — intercooler cleaning and servicing require additional clearance. The installation layout must allow space for cooler core extraction or access-panel opening.
FAQ
What pressure options does DUALLUBE offer?
DUALLUBE two-stage compressors are available in 8, 10 and 13 bar. The exact model row and FAD at each pressure are given on the current datasheet.
Is DUALLUBE the same as SILVERLUBE?
No. DUALLUBE is a two-stage oil-lubricated screw compressor. SILVERLUBE is a single-stage oil-lubricated screw compressor. They serve different parts of the pressure/flow range and are selected on different criteria. Two-stage and single-stage model tables are not interchangeable.
How much electricity does two-stage save vs single-stage?
The saving depends on the pressure ratio and operating conditions. As a general industry reference, two-stage compression reduces specific power by 5–15% compared with single-stage at rated conditions. The actual figure depends on the specific pressure ratio, model and duty cycle.
Does the intercooler add maintenance burden?
The intercooler adds one additional maintenance point compared with a single-stage machine. For air-cooled intercoolers, the maintenance task is straightforward — periodic cleaning of the cooling fins. When maintenance is carried out to schedule, the intercooler does not become a source of failures.
Why are 22–37 kW only available in low-pressure?
This is a product-positioning decision. At smaller power ratings, standard-pressure requirements are covered by the SILVERLUBE S single-stage range. DUALLUBE D begins at 45 kW for standard pressures (8 / 10 / 13 bar).
More questions
What is the difference between VPM-B and VPM?
VPM-B is the low-pressure variant of the variable-frequency drive, optimised specifically for 4–5 bar(g) applications. Both VPM and VPM-B use the same variable-frequency drive principle, but they have different rotor profiles and inter-stage pressure-ratio allocation. They are not interchangeable — each must be selected for its intended pressure range.
Ownership & service
Energy, maintenance and service
Energy Savings Framework
Calculating the energy savings from two-stage compression requires a comparison between single-stage and two-stage performance at the specific operating conditions:
Typical assumptions (for estimation, not a commitment):
SIND can provide a project-specific single-stage vs two-stage energy comparison at quotation stage, based on the customer’s load profile or operating shift pattern.
- Two-stage specific power is 5–15% lower than single-stage (depending on pressure ratio and model).
- For applications running 6,000–8,000 hours per year, payback is typically 2–4 years.
- Higher annual operating hours shorten the payback period.
- Higher electricity prices shorten the payback period.
Two-stage annual consumption = Σ (two-stage input power per load segment × hours at that segment)
Single-stage annual consumption = Σ (single-stage input power per load segment × hours at that segment)
Annual energy saving = single-stage annual consumption − two-stage annual consumption
Annual cost saving = annual energy saving × local electricity price
Payback period = (two-stage purchase cost − single-stage purchase cost) / annual cost savingMaintenance Cost Structure
DUALLUBE D maintenance items are similar to SILVERLUBE S, with one additional key component — the intercooler:
The intercooler is a maintenance item unique to two-stage machines. Air-cooled intercoolers require periodic fin cleaning; water-cooled units need monitoring for scale build-up on the water side. Specific maintenance intervals follow the operator manual supplied with the machine.
| Maintenance item | Typical interval | Notes |
|---|---|---|
| Oil-separator element | 2,000–4,000 h | Replace when differential pressure reaches set value |
| Lubricating oil | 4,000–8,000 h | Two-stage machines may use a larger oil charge than single-stage |
| Oil filter | 2,000–4,000 h | Replace together with oil |
| Air filter | 1,000–2,000 h | Depends on ambient dust concentration |
| Intercooler | 8,000–16,000 h | Clean or inspect; depends on cooling-water quality or airflow conditions |
Service
The same service support framework as SILVERLUBE S. Because two-stage machines are more complex, it is recommended to agree a maintenance contract at the time of purchase, ensuring that key components such as the intercooler receive professional servicing.
