Product Overview: ZW Series Unloading Air Compressor
The ZW series unloading air compressor is a vertical-frame (Z-type) oil-free reciprocating piston compressor for industrial instrument air, process air, food-grade compressed air, and high-pressure air supply applications requiring guaranteed oil-free output. Two design features define this product: the oil-free compression principle, achieved through PTFE (polytetrafluoroethylene) self-lubricating piston rings and packing that operate without any oil at the cylinder wall; and the suction valve unloading capacity control system, which allows the compressor to reduce output from full capacity to partial load or zero load by mechanically holding the suction valves open, without stopping and restarting the motor.
Oil-free by design means something specific and different from oil-injected-with-filtration: there is no lubricating oil in the compression cylinder at any point in the operating cycle. The PTFE rings slide against the cylinder wall without oil, producing compressed air that contains zero oil aerosol, zero oil vapour, and zero oil mist — down to Class 0 oil content per ISO 8573-1 at the compressor outlet. This is the air quality required by food and beverage processing lines, pharmaceutical manufacturing, electronics assembly, instrument air networks supplying control valve actuators, painting and surface coating lines, and laboratory supply where oil contamination at any concentration would be unacceptable.
The suction valve unloading system is the practical solution to the variable compressed air demand problem. Most compressed air systems operate at variable load: a factory instrument air header needs full flow during a production shift, partial flow during changeover, and near-zero flow during maintenance stops. Starting and stopping the motor repeatedly to match demand accelerates motor winding wear, mechanical fatigue at the motor terminals, and gas valve wear in the compressor. Suction valve unloaders hold the suction valves open mechanically so that air drawn into the cylinder on the suction stroke is simply pushed back out without being compressed — the motor continues running at the same speed but the compressor produces no compressed air and consumes only a fraction of full-load power (typically 15–25%). 13 standard models cover 1.5–20 m³/min at 0.70–3.00 MPa, all at 380 V. GOST-R certified for Russia and CIS, manufactured at our production facility in Russia.
Technical Specifications — Low and Medium Pressure (0.70–1.00 MPa)
Standard compressed air supply range for instrument air headers, process air, pneumatic tools, conveying systems, and general industrial compressed air at 7–10 bar. All models: PTFE oil-free rings, 380 V, suction-valve unloading standard.
| Model |
Config |
Flow (m³/min) |
Discharge (MPa) |
Dimensions L×W×H (mm) |
Weight (t) |
Power (kW) |
Voltage |
| ZW-1.5/8-A |
2-col 2-stage |
1.5 |
0.80 |
720×763×1274 |
0.58 |
15 |
380 |
| ZW-2/7-A |
2-col 2-stage |
2.0 |
0.70 |
720×763×1475 |
0.38 |
18.5 |
380 |
| ZW-3/7-A |
2-col 2-stage |
3.0 |
0.70 |
720×763×1274 |
0.58 |
22 |
380 |
| ZW-4.8/8-A |
2-col 2-stage |
4.8 |
0.80 |
2250×1296×2350 |
2.00 |
37 |
380 |
| ZW-5.3/8-A |
2-col 2-stage |
5.3 |
0.80 |
2250×1865×2350 |
2.00 |
45 |
380 |
| ZW-6/8-A |
2-col 2-stage |
6.0 |
0.80 |
2250×1296×2350 |
2.00 |
45 |
380 |
| ZW-20/10-A |
2-col 2-stage |
20.0 |
1.00 |
2764×2000×2600 |
5.00 |
160 |
380 |
Suffix /7 = 0.70 MPa, /8 = 0.80 MPa, /10 = 1.00 MPa. All models include suction-valve unloading for capacity control. Dimensions L×W×H in mm. Smallest models (0.58 t) can be installed without a crane.
Technical Specifications — Mid-High Pressure (1.50–3.00 MPa)
Multi-stage configurations for high-pressure instrument air, PET bottle blowing pre-compression, high-pressure testing air, and compressed air at 15–30 bar. The 3ZW three-column model provides higher flow at 3.0 MPa in the same envelope.
| Model |
Config |
Flow (m³/min) |
Discharge (MPa) |
Dimensions L×W×H (mm) |
Weight (t) |
Power (kW) |
Voltage |
| ZW-6/15-A |
2-col 2-stage |
6.0 |
1.50 |
2280×950×1170 |
1.80 |
65 |
380 |
| ZW-10/15-A |
2-col 2-stage |
10.0 |
1.50 |
2790×1500×2590 |
3.00 |
110 |
380 |
| ZW-4/30-A |
2-col 3-stage |
4.0 |
3.00 |
1920×1900×2825 |
4.00 |
55 |
380 |
| 3ZW-9.5/30-A |
3-col 3-stage |
9.5 |
3.00 |
1845×1660×2360 |
3.50 |
110 |
380 |
| ZW-13/30-A |
2-col 3-stage |
13.0 |
3.00 |
2764×2000×3277 |
6.00 |
160 |
380 |
Suffix /15 = 1.50 MPa (15 bar), /30 = 3.00 MPa (30 bar). 3ZW-9.5/30-A: 3-column frame provides more flow at 3.0 MPa without increasing machine height. All dimensions L×W×H in mm.
General Series Parameters
| Parameter |
ZW Series Specification |
| Compression Medium |
Atmospheric air; filtered intake air (ISO 8573-1 Class 0 oil output) |
| Discharge Pressure |
0.70–3.00 MPa (7–30 bar) |
| Flow Range |
1.5–20 m³/min (90–1,200 m³/h) |
| Motor Power |
15–160 kW |
| Drive Voltage |
380 V throughout — all 13 models |
| Frame Configuration |
Vertical (Z-type); 2-column (ZW) or 3-column (3ZW); 2 or 3 stages |
| Machine Weight |
0.38–6.00 t |
| Lubrication |
Oil-free by design — PTFE piston rings and packing, no oil at cylinder wall |
| Capacity Control |
Suction valve unloading — 100% and 0% (or step-wise with multiple unloaders) |
| Air Quality (outlet) |
ISO 8573-1 Class 0 oil content; downstream filter and dryer as required for full ISO class |
| Cooling |
Water-cooled standard (intercoolers and aftercooler); air-cooled option for remote sites |
| Design Standard |
JB/T 10683-2006 (oil-free lubricated medium and high pressure air compressors); GOST-R |
| Certification |
ISO 9001:2015, GOST-R, Pressure Vessel License |
Working Principle: Oil-Free Compression and Suction Valve Unloading
The ZW series uses vertical reciprocating piston compression. The motor drives a horizontal crankshaft; the cylinders project vertically from the crankcase. Air enters through a suction filter on the intake stroke, is compressed through one or more stages, and exits through an aftercooler and receiver to the downstream air system. The defining oil-free feature is in the cylinders: PTFE (polytetrafluoroethylene) piston rings fit directly onto the piston and run against the bore in a dry, oil-free contact. PTFE’s low coefficient of friction — among the lowest of any solid material — allows sustained dry sliding at the cylinder wall temperature and surface speed of reciprocating compression without requiring liquid lubrication. The result is compressed air with zero oil at the compressor cylinder outlet, without any downstream oil removal filtration stage.
The suction valve unloading system addresses the variable-demand problem. Suction unloaders are small electro-pneumatic actuators that hold the suction valves mechanically open during the compressor’s suction stroke. When held open, the suction valve does not close at the start of the compression stroke — so air drawn in on the suction stroke is pushed back out through the open suction valve rather than being compressed. The cylinder does mechanical work on the air on the compression stroke but delivers none to the system — the compressor produces zero output while the motor continues running. Unloading power consumption is typically 15–25% of full-load power, compared to 60–70% for a motor idling on a speed controller at minimum speed. For duty cycles where compressed air demand is zero for extended periods (shift changeover, cleaning cycles, process interruptions), suction valve unloading is more energy-efficient than continuous partial-speed operation on a VFD.
PTFE Piston Rings
Self-lubricating PTFE rings run dry against the cylinder bore at all times. No oil injection, no oil reservoir in the cylinder, no oil separator required downstream. Ring service life 4,000–6,000 hours in clean, dry air service. Replacement from ground level without cylinder disassembly.
Suction Valve Unloaders
Electro-pneumatic or spring-loaded actuators on the suction valves hold valves open on demand. Controlled by pressure switch or PLC. Transition between loaded and unloaded states in under 2 seconds. No motor start-stop, no inrush current surge, no mechanical shock at gas valves on cycling.
Interstage Cooling
Water-cooled intercoolers between each stage remove heat of compression and condensed moisture before the next stage inlet. Aftercooler on the final discharge. Condensate drain on each cooler. Lower stage inlet temperatures improve volumetric efficiency and reduce PTFE ring operating temperature.
Vertical Frame — Small Footprint
Cylinders stack vertically above the horizontal crankshaft. The smallest ZW models (0.38–0.58 t) occupy a floor area of less than 1 m² and can be installed in a standard equipment room without specialist handling. Gravity-assisted piston ring seating in the vertical orientation reduces ring side-loading and extends PTFE ring life.
Application Scenarios
⚙ Instrument Air Systems
Control valve actuators, positioners, analysers, and pneumatic instruments require clean, dry, oil-free air at 0.5–0.8 MPa. Oil contamination of a pneumatic positioner diaphragm or a valve actuator seal causes stiction, incorrect valve positioning, and process upsets. The ZW-3/7-A through ZW-6/8-A cover the instrument air flow range of small-to-medium Russian industrial plants with a dedicated oil-free supply independent of the general industrial air header.
🍲 Food, Beverage, and Pharmaceutical
Food processing, beverage filling, pharmaceutical tableting, and cosmetics packaging lines use compressed air in direct contact with product — for blowing, conveying, filling, and sealing. Oil in compressed air contaminates food product, invalidates pharmaceutical batch records, and causes regulatory non-compliance. ISO 8573-1 Class 0 oil content at the ZW compressor outlet satisfies the oil-free requirement without downstream oil removal filtration.
⚙️ Electronics and Precision Manufacturing
PCB assembly lines, semiconductor clean rooms, optical component production, and precision metrology use oil-free compressed air for component handling, pneumatic actuators, and air bearings. Oil vapour deposition on PCBs or optical surfaces causes adhesion failures and coating defects. The ZW series provides oil-free air at the source without relying on activated carbon filters that require frequent replacement and monitoring.
🌊 High-Pressure Air — PET Blowing and Testing
PET bottle blowing requires air at 2.5–3.5 MPa for the final blow-moulding step. The ZW-4/30-A, 3ZW-9.5/30-A, and ZW-13/30-A provide 30-bar oil-free air for PET blowing machines at medium-scale production facilities. High-pressure air testing (pneumatic pressure tests on vessels, valves, and pipework) uses the same pressure range; oil-free supply prevents contamination of test components that will subsequently be used in clean service.
Core Advantages
📈
ISO 8573-1 Class 0 Oil at the Source
No oil is present in the compression cylinder at any point. The ZW delivers Class 0 oil content at the compressor outlet before any downstream filtration. Oil-injected compressors with coalescing filters deliver Class 1 at best — and filter performance degrades over time between service intervals.
⚡
Suction Valve Unloading — No Motor Cycling
Motor continues running at constant speed during unloaded periods. No start-stop surge current, no mechanical shock to gas valves, no thermal cycling of motor windings. Motor life is determined by bearing hours at constant speed, not by the number of start-stop cycles that accelerate winding insulation fatigue in cycling applications.
🕑
380 V Across the Full Range
Every ZW model from 15 kW to 160 kW runs at 380 V. No high-voltage supply, no dedicated transformer, no 6 kV or 10 kV switchgear. Directly compatible with standard Russian and CIS industrial three-phase supply at any installation site.
🔌
Small Footprint — Installs Anywhere
The smallest ZW models weigh 0.38–0.58 t and occupy less than 1 m² of floor area. The largest model (ZW-13/30-A at 6.0 t, 2.76 m x 2.0 m) is smaller than a typical oil-injected screw compressor package of comparable output. Vertical frame makes use of ceiling height rather than floor area.
📄
GOST-R Certified for Russia and CIS
GOST-R certificate, technical passport, and pressure vessel certification for all interstage coolers and the aftercooler, provided as standard with every ZW unit. All documentation in Russian. Manufactured at our production facility in Russia — no import logistics, no foreign currency exposure.
🌎
Russia-Based PTFE Spare Parts
PTFE piston rings, packing, and gas valve elements for all ZW-A models stocked in-house at our Russian facility. Dispatch within 24–72 hours. No import wait for maintenance-critical parts. PTFE ring replacement is a half-day job that does not require specialist tooling or disassembling the machine.
Material Specifications
| Component |
Specification |
| Cylinders |
HT250 grey cast iron with water jackets; liner replaceable for re-bore service |
| Piston Rings |
PTFE self-lubricating — no oil at cylinder wall; service life 4,000–6,000 hours in clean dry air |
| Piston Rod Packing |
PTFE pressure packing rings; single-compartment vented packing box |
| Piston Rods |
42CrMo alloy steel, hard chrome plated; ground and polished to H6 tolerance |
| Gas Valves |
Stainless steel ring-plate or poppet valves; PTFE or PEEK valve elements; service life 8,000–10,000 hours |
| Intercoolers / Aftercooler |
Shell-and-tube, carbon steel shell, stainless steel tubes; automatic condensate drain |
| Crankshaft |
Forged 42CrMo; hardened and ground journals; splash-lubricated in crankcase (oil does not enter cylinders) |
| Suction Valve Unloaders |
Electro-pneumatic actuators; controlled by pressure switch or PLC; response time under 2 seconds |
Selection Guide
1
Confirm that oil-free air is required at the point of use — not all compressed air applications need oil-free supply. Pneumatic tools, general conveying, and non-contact industrial air can tolerate ISO 8573-1 Class 1 or Class 2 oil content, which oil-injected screw compressors with coalescing filters can provide at lower capital cost. Oil-free air at the source is required when the air contacts food, pharmaceutical product, electronics, instrument components, or when oil carryover would cause regulatory non-compliance or equipment damage.
2
Specify peak demand flow and average demand flow separately — the compressor is sized for peak demand flow (the maximum flow the system needs at any point). Average demand determines whether suction valve unloading is the right control strategy. If average demand is consistently above 80% of peak, suction valve unloading provides little benefit over continuous operation — VFD speed control is more appropriate. If average demand frequently drops to 50% or below, suction valve unloading reduces motor starts and unloading power loss.
3
Confirm the downstream air quality requirement — the ZW compressor provides Class 0 oil at the compressor outlet. Additional downstream treatment — refrigerant dryer for moisture (ISO 8573-1 Class 4 moisture standard), activated carbon filter for residual hydrocarbon (Class 1), and final particulate filter (Class 1) — is required to reach the full ISO 8573-1 Class 1.2.1 specification for pharmaceutical and food-grade applications. State the required ISO 8573-1 class at enquiry so the downstream treatment scope can be included in the proposal.
ZW vs. Oil-Injected Screw Compressor: Objective Comparison
Transparency Notice: Atlas Copco, Kaeser, and Ingersoll Rand are referenced for product category comparison only. We do not manufacture or claim affiliation with these brands. All ZW compressors are original designs. We do not sell counterfeit or unlicensed products.
| Factor |
ZW Oil-Free Reciprocating |
Oil-Injected Screw + Filters |
Oil-Free Screw (water-injected) |
| Oil at outlet |
ISO 8573-1 Class 0 |
Class 1 (filter-dependent) |
Class 0 (design) |
| Max discharge pressure |
3.0 MPa (30 bar) |
1.3 MPa typical |
1.0 MPa typical |
| Oil carryover risk |
Zero by design |
Present if filter bypasses |
Zero by design |
| Capital cost |
Lower than oil-free screw |
Lowest |
Highest |
| 380 V / all-Russian supply |
✓ All models |
✓ Most models |
✓ Most models |
| Russian spare parts |
In-house Russia stock |
Import typically |
Import typically |
| GOST-R standard |
✓ Included |
Case by case |
Case by case |
Factory run test — every ZW series air compressor is operated at rated conditions to verify oil-free output, suction valve unloading response, and discharge pressure before shipment from our Russian facility
Frequently Asked Questions
Q1: What is the difference between oil-free by design and oil-injected with filtration?
Oil-injected screw compressors inject lubricating oil into the compression chamber to cool and seal the rotors, then use a sequence of oil separators and coalescing filters to remove oil from the compressed air before delivery. Even with high-efficiency filters, a residual oil aerosol at concentrations of 0.01–0.1 mg/m³ (ISO Class 1) passes through. If the coalescing filter element fails or is not replaced on schedule, oil carryover rises immediately. Oil-free by design — as in the ZW series — means no oil is present in the compression cylinder at any point. PTFE rings run dry; there is no oil to carry over, regardless of downstream filter condition. ISO 8573-1 Class 0 oil output at the compressor outlet is a structural property of the machine, not dependent on filter maintenance.
Q2: How does suction valve unloading work and how is it controlled?
Suction valve unloaders are small actuators mounted on each suction valve that hold the valve disc away from its seat throughout the entire suction and compression stroke. With the suction valve held open, air drawn in during the suction stroke is simply pushed back out through the open suction valve during the compression stroke — no compression occurs, no air is delivered to the receiver. The motor continues running at rated speed and consumes only the mechanical friction losses of the crankshaft and pistons — typically 15–25% of full-load power. Control is via a pressure switch on the air receiver: when receiver pressure rises to the upper set point, the PLC energises the unloader solenoid valves and the compressor enters unloaded running. When receiver pressure falls to the lower set point, the PLC de-energises the unloaders and the compressor returns to full compression within 2–3 crankshaft revolutions. The cycle can repeat many thousands of times per day with no mechanical wear consequence — there is no motor start current, no thermal shock to the motor windings, and no sudden pressure transient at the gas valves.
Q3: What is the PTFE ring service life and how do I know when to replace them?
PTFE piston ring service life in clean, dry atmospheric air is typically 4,000–6,000 operating hours. The principal wear mechanism is abrasive wear from particulate matter in the inlet air — which is why inlet air filtration quality directly affects ring life. With a standard 10-micron inlet filter, life is at the 4,000–5,000 hour end; with a 3-micron inlet filter, life approaches 6,000 hours. The practical indicator of PTFE ring wear is increasing oil-in-air measurement at the outlet (if measured) or, more practically, increasing cylinder discharge temperature on that stage. As rings wear and bypass increases, volumetric efficiency falls and discharge temperature rises. A 10°C rise above the baseline discharge temperature at the same ambient conditions and the same pressure is the typical trigger for ring inspection. Full ring replacement takes approximately 3–5 hours per cylinder from a trained maintenance team. All PTFE ring sets are available from our Russian facility with 24–72 hour dispatch.
Q4: Does the ZW compressor require a water supply for cooling?
Standard ZW models are water-cooled, requiring a clean water supply to the intercoolers and aftercooler. Water consumption at the intercoolers is modest — typically 0.5–2 m³/h for a 45–160 kW machine depending on the number of stages and ambient temperature. Cooling water can be recirculated in a closed loop with a cooling tower or plate cooler if a once-through supply is not available. For remote sites or installations where water supply is not available, an air-cooled variant with fan-assisted intercoolers can be supplied — this reduces water consumption to zero at the cost of a slightly larger footprint and higher ambient temperature sensitivity. Specify the cooling method at enquiry.
Q5: What downstream air treatment is needed after the ZW compressor to reach ISO 8573-1 Class 1?
The ZW compressor provides Class 0 oil content at the outlet. To reach the full ISO 8573-1 Class 1.2.1 standard (the specification for food-grade and pharmaceutical air), two additional treatment steps are typically required. A refrigerant air dryer reduces moisture to a pressure dew point of −3°C or below (ISO moisture Class 4), removing the bulk of condensed water that the interstage and aftercooler have not separated. A final coalescing and particulate filter removes solid particles to Class 1 (0.1 micron). If residual hydrocarbons from ambient air are a concern — as in chemical plant environments — an activated carbon adsorber downstream of the refrigerant dryer removes hydrocarbon vapours to below 0.01 mg/m³. None of these downstream components introduce oil into the air system; they only remove what was in the atmospheric air at intake.
Q6: What maintenance does the ZW air compressor require annually?
Annual maintenance for a ZW air compressor in normal industrial service typically covers: inlet air filter element replacement (every 1,000–2,000 hours depending on site dust level); gas valve inspection and element replacement if wear is observed (8,000–10,000 hour life under clean air conditions); PTFE piston ring inspection at 4,000 hours and replacement if wear exceeds the allowable limit; crankcase oil change (every 1,000 hours or annually, whichever is sooner — note that the crankcase oil lubricates the crankshaft and connecting rod bearings only and does not enter the cylinders); intercooler and aftercooler condensate drain check; and suction valve unloader actuator function test. The PTFE rings, gas valve elements, and inlet filter elements are the consumable maintenance items. All are available from our Russian facility within 24–72 hours of order.
Q7: Can the ZW series operate at high altitude or in cold climate conditions?
Yes, with appropriate specification at the design stage. At high altitude (above 1,000 m), inlet air density is lower, and the volumetric flow in m³/min remains the same as at sea level but the mass flow and pressure at discharge fall proportionally. For installations at altitudes above 1,000 m, state the site altitude at enquiry so the performance can be derated correctly — the compressor may need to be one model size larger to achieve the required mass flow at altitude. For cold climate operation (Siberian and Central Asian installations at ambient temperatures as low as −40°C), arctic-grade crankcase oil, heated start-up systems for the cooling water circuit, and cold-climate motor insulation are required; these are available as standard options for Russian far-north installations. GOST-R certification covers operation in the standard Russian climate range.
Q8: What is the delivery time and what spare parts should be stocked on-site?
Standard delivery from confirmed purchase order is 3–5 months for ZW air compressor models — shorter than gas and hydrogen compressor deliveries because of the simpler material specification (no ATEX, no copper-free requirement, no NACE materials) and the lighter machine weight. The recommended on-site stock for a ZW air compressor includes: one complete PTFE piston ring and packing set for each cylinder stage (supporting the machine through two ring replacements over the first 10,000 hours), one set of gas valve elements for each cylinder position, one inlet filter element, and a set of suction valve unloader actuator seals. This stock fits in a standard parts cabinet and is typically consumed over two years of normal operation. All parts available from our Russian facility with 24–72 hour dispatch.
Q9: Can a VFD replace the suction valve unloading system?
A variable frequency drive (VFD) and suction valve unloading solve the variable demand problem in different ways and suit different duty profiles. VFD provides continuous smooth modulation of compressor speed from approximately 50–100% of rated flow, with proportionally reduced power at partial speed — best when demand varies continuously and smoothly, as in a large plant instrument air header with many simultaneous users. Suction valve unloading provides binary on/off control (or step-wise in multi-stage models) — best when demand drops sharply to near-zero during clearly defined periods such as shift changes or maintenance stops. VFD has higher capital cost but better energy efficiency at continuously variable load. Suction valve unloading has lower capital cost and zero part-load speed, which reduces mechanical wear at low load but consumes more power than VFD at intermediate loads. The ZW series can be supplied with either control method, or with both in combination for maximum flexibility.
Q10: What GOST-R documentation is provided with ZW air compressors?
Every ZW series air compressor delivered to Russia or CIS member states is supplied with: GOST-R certificate of conformity, technical passport with all rated performance parameters and cylinder specifications, pressure vessel certification for all interstage coolers and the aftercooler (required for vessels operating above 0.07 MPa), factory run test report confirming oil-free output and discharge pressure performance, and Russian-language operating and maintenance manual. Air compressors in Russia do not require Rostechnadzor registration as hazardous production facilities unless they are part of a system classified as dangerous equipment under Federal Law 116-FZ. Standard industrial compressed air supply for instrument air and process air is not subject to this registration requirement. The GOST-R documentation package we provide is sufficient for normal commissioning and operation of industrial compressed air systems in Russia and all EEU member states.
Request a Technical Proposal
Our engineering team supplies ZW series unloading air compressors to food processing facilities, pharmaceutical manufacturers, electronics plants, and industrial instrument air systems across Russia and the CIS. Oil-free by design, suction valve unloading for variable demand, 380 V throughout, GOST-R certified, and spare parts in Russia with 24–72 hour dispatch.
ZW Unloading Air Compressor — Engineering Enquiry
Discuss Your Oil-Free Compressed Air Requirement
Compressor engineers respond to all enquiries. GOST-R documentation included. Response within 48 hours.
Request a Technical Quote
Include in Your Enquiry
✓ Required flow (m³/min or m³/h)
✓ Discharge pressure (MPa or bar)
✓ ISO 8573-1 air quality class required
✓ Demand profile (continuous or variable)
✓ Cooling method (water or air)
✓ Site altitude and ambient temperature range
✓ GOST-R documentation required
✓ Required delivery date
