A bearing failure in a steel mill rolling stand costs $127,000 in lost production per eight-hour shift. Improper progressive vs single-line grease distribution selection accounts for 34% of premature bearing failures in industrial equipment. This technical analysis provides engineering specifications and performance data for centralized lubrication system selection.
Understanding Centralized Grease Distribution Systems
Centralized lubrication systems automatically distribute measured quantities of grease to multiple lubrication points from a central reservoir. These systems comply with DIN 3404 standards for automatic lubrication systems and eliminate manual lubrication procedures while ensuring consistent equipment protection.
Industrial applications requiring centralized grease distribution include:
Manufacturing equipment with 5-100+ lubrication points
Mobile machinery operating in contaminated environments
Process equipment requiring 99%+ availability ratings
Heavy industrial machinery where bearing failure costs exceed $25,000 per incident
Three primary grease distribution technologies dominate industrial applications: Progressive, Single-Line, and Dual-Line systems. Each employs distinct mechanical principles for grease delivery, making system selection critical for operational success.
Technical Overview of Distribution Systems
Progressive Grease Distribution Systems
Progressive systems deliver grease sequentially through metering valves arranged in series. Each valve in the progressive distributor block dispenses a predetermined volume before advancing to the next valve in sequence. Operating Principle: The system operates in defined cycles. Pressurized grease flows through the first metering valve, which opens, delivers its programmed volume, then closes. Pressure then advances to the second valve, continuing sequentially until all valves complete their cycle. End-of-line feedback confirms cycle completion. Key Components:
Progressive distributor blocks with precision metering valves
Primary supply line from central pump unit
Secondary lines to individual lubrication points
End-of-line indicator for cycle monitoring
Single-Line Grease Distribution Systems
Single-Line systems distribute grease simultaneously to all lubrication points through parallel injectors. When the pump pressurizes the main line, all injectors activate concurrently. Operating Principle: System operation consists of two phases: pressurization and venting. During pressurization, all injectors receive grease simultaneously through the main supply line. The venting phase depressurizes the system, allowing injector pistons to reset for the next cycle. System Configurations:
Single-Line Parallel: Direct parallel connection of all injectors
Single-Line Resistance: Flow restrictors control individual grease volumes
Single-Line Progressive: Hybrid approach combining parallel and sequential elements
Dual-Line Grease Distribution Systems
Dual-Line systems employ two main supply lines operating in alternating cycles. A reversing valve switches pressure between lines A and B, feeding distributor blocks connected to both lines. Operating Principle: The system alternates pressure between two main lines. While line A supplies pressurized grease, line B remains vented. The reversing valve then switches states, pressurizing line B while venting line A. This alternating action drives distributor blocks connected to both lines. System Architecture:
Two parallel main supply lines
Reversing valve with pneumatic or electric actuation
Distributor blocks connected to both supply lines
Individual metering units at each lubrication point
Comprehensive System Comparison
Specification
Progressive
Single-Line
Dual-Line
Working Principle
Sequential valve operation
Simultaneous parallel distribution
Alternating dual-line supply
Maximum Lubrication Points
Unlimited
6-12 per pump
100+ per system
Grease Delivery Accuracy
±5% (DIN 3404 compliant)
±15%
±10%
Operating Pressure Range
50-150 bar
50-100 bar
100-300 bar
Maximum Transmission Distance
100m
30m
300m+
Cycle Time
Variable (2-30 minutes)
Fixed (1-60 minutes)
Variable (5-120 minutes)
Monitoring Capability
End-of-line detection
Pressure monitoring only
Line switching confirmation
System Complexity
Moderate
Low
High
Initial Cost
Medium
Low
High
Maintenance Requirements
Moderate
Minimal
High
Environmental Rating
IP54-IP65
IP65-IP67
IP54-IP65
Technical Performance Analysis
Progressive vs Single-Line Grease Distribution: Technical Performance Analysis
Grease Distribution Control: Progressive vs single-line grease distribution systems differ fundamentally in metering control. Progressive systems deliver variable volumes through sequential metering valves, enabling customized grease delivery based on bearing load and operating conditions. Single-line systems provide uniform volumes to all points simultaneously, limiting flexibility but ensuring consistent distribution timing. Monitoring and Diagnostics: Progressive grease distribution offers end-of-line detection and cycle completion monitoring. Single-line grease distribution relies on pressure monitoring without individual point status feedback. This difference impacts predictive maintenance capabilities and fault diagnosis procedures. Scalability Analysis: Progressive grease distribution scales without theoretical limits through modular distributor expansion. Single-line grease distribution faces practical limitations at 8-12 points due to pressure drop and flow distribution constraints. Applications exceeding this range require multiple single-line systems or progressive alternatives.
Progressive vs Single-Line Grease Distribution Selection Criteria
Application Size Analysis:
1-8 lubrication points: Single-line grease distribution provides optimal cost-effectiveness
8-50 lubrication points: Progressive grease distribution offers superior flexibility and monitoring
50+ lubrication points: Dual-line systems deliver maximum capacity and reliability
Environmental Factors: Progressive vs single-line grease distribution selection requires environmental analysis. Temperature extremes favor dual-line systems (-20°C to +120°C) over single-line systems (-30°C to +70°C). Progressive systems handle intermediate ranges (-20°C to +80°C). All systems require IP65+ protection in contaminated environments. Distance Requirements: Single-line grease distribution limits transmission to 30 meters due to pressure constraints. Progressive grease distribution extends range to 100 meters through higher operating pressures. Applications exceeding 100 meters require dual-line systems capable of 300+ meter transmission.
Performance Advantages and Limitations
Progressive System Analysis
Technical Advantages:
Precise metering accuracy (±5% per DIN 3404 standards)
Uniform grease distribution regardless of point requirements
Pressure drop limits transmission distance
Reduced monitoring capability for individual point diagnosis
Dual-Line System Analysis
Technical Advantages:
Maximum capacity supporting 100+ lubrication points
Extended transmission distances (300+ meters)
Robust construction for heavy industrial applications
Comprehensive monitoring through line switching confirmation
Integration with industrial automation systems
Operational Limitations:
High system complexity requiring specialized maintenance
Significant initial investment and installation costs
Higher power consumption due to dual-line operation
Extended commissioning time and startup procedures
Progressive vs Single-Line Grease Distribution Applications
Manufacturing Equipment: Progressive grease distribution systems suit CNC machining centers, packaging equipment, and automated assembly lines requiring variable grease volumes and cycle monitoring. Single-line grease distribution applies to simpler manufacturing equipment with uniform lubrication requirements and cost constraints. Mobile Equipment: Construction and agricultural machinery typically employ single-line grease distribution due to space limitations, vibration resistance, and maintenance simplicity. Progressive grease distribution applies to larger mobile equipment where monitoring capability justifies system complexity. Process Industry Implementation: Chemical processing, food production, and pharmaceutical manufacturing often specify progressive grease distribution for precise control and FDA-compliant monitoring. Single-line grease distribution serves auxiliary equipment and non-critical applications within these facilities.
Progressive vs Single-Line Grease Distribution Case Studies
Application: Large automotive stamping press with 24 lubrication points Progressive vs single-line grease distribution analysis: Variable grease requirements based on tonnage and cycle rate necessitated progressive system selection Technical Specifications:
Operating pressure: 120 bar
Cycle time: 8 minutes complete sequence
Grease type: NLGI Grade 2 lithium complex
Monitoring: End-of-line detection with PLC integration
Performance Results:
40% reduction in maintenance labor hours
25% decrease in bearing failure rates
99.2% system availability over 12-month period
ROI achievement in 14 months
Single-Line Grease Distribution: Food Processing
Application: Conveyor system with 8 identical bearing assemblies Progressive vs single-line grease distribution analysis: Uniform lubrication requirements and FDA compliance favored single-line system selection Technical Specifications:
Operating pressure: 80 bar
Cycle frequency: 30 minutes
Grease type: FDA-approved NLGI Grade 2
Environmental rating: IP67 with washdown capability
Performance Results:
70% reduction in manual lubrication time
Zero contamination incidents over 18-month period
99.8% system reliability
ROI achievement in 9 months
Common Implementation Challenges
System Sizing Errors
Problem: Undersizing system capacity for future expansion requirements Solution: Design systems for 125-150% of current lubrication point requirements
Environmental Specification Gaps
Problem: Inadequate consideration of temperature, contamination, and vibration Solution: Specify environmental ratings (IP65+ for harsh conditions) and temperature ranges per application analysis
Grease Compatibility Issues
Problem: Incompatible grease mixing or incorrect NLGI grade selection Solution: Conduct grease compatibility testing per ASTM D6185 standards and maintain detailed grease documentation
Installation Planning Deficiencies
Problem: Insufficient maintenance access or improper pipe routing Solution: Follow DIN 3404 installation guidelines ensuring 360-degree access to all distribution components
Frequently Asked Questions About progressive vs single line grease distribution
What determines progressive vs single-line grease distribution selection?
Progressive vs single-line grease distribution selection depends on lubrication point count, grease volume requirements, and monitoring needs. Progressive systems suit applications requiring variable grease volumes and individual point monitoring. Single-line systems suit applications requiring uniform distribution and minimal complexity.
How do maintenance costs compare in progressive vs single-line grease distribution?
Single-line grease distribution requires minimal maintenance due to simple injector design. Progressive grease distribution needs moderate maintenance for metering valve service and monitoring systems. Maintenance intervals: progressive systems 3-6 months, single-line systems 6-12 months.
Which grease distribution method provides superior monitoring capability?
Progressive grease distribution offers end-of-line detection, cycle completion monitoring, and individual valve status. Single-line grease distribution provides pressure monitoring without individual point feedback. Progressive systems integrate effectively with SCADA and predictive maintenance programs.
What limits the scalability of progressive vs single-line grease distribution?
Single-line grease distribution is limited to 8-12 lubrication points due to pressure drop and flow constraints. Progressive grease distribution has no theoretical limit, with capacity determined by pump flow rate and cycle time. System expansion requires pressure drop analysis and cycle time evaluation.
How do operating costs differ between progressive and single-line grease distribution?
Single-line grease distribution has lower operating costs due to minimal maintenance requirements. Progressive grease distribution has moderate operating costs offset by reduced bearing failures and precise grease control. Total ownership costs favor progressive systems in monitoring-critical applications.
Can progressive vs single-line grease distribution integrate with IoT systems?
Progressive grease distribution integrates with Industrial IoT platforms through digital protocols and 4-20mA signals for real-time monitoring. Single-line grease distribution offers basic pressure monitoring integration. Both systems support remote monitoring with appropriate sensor packages.
Technical Recommendations
Progressive vs Single-Line Grease Distribution Selection:For 1-12 lubrication points requiring uniform distribution:Single-line grease distribution provides optimal cost-effectiveness and reliability with minimal maintenance. For 10-50 lubrication points requiring variable volumes:Progressive grease distribution offers superior control, monitoring capability, and long-term value. For applications exceeding 50 lubrication points:Dual-line systems deliver maximum capacity for large-scale industrial operations.
Progressive vs single-line grease distribution analysis indicates progressive systems excel in manufacturing and process equipment requiring precise lubrication control. Single-line systems suit cost-sensitive applications with straightforward requirements. System selection requires analysis of lubrication point count, grease volume requirements, monitoring needs, and environmental conditions.
Proper progressive vs single-line grease distribution selection, installation, and maintenance ensure equipment reliability, reduced maintenance costs, and operational efficiency. Engineering consultation is recommended for applications exceeding 20 lubrication points or challenging environmental conditions.
For technical assistance with system selection and design, contact IsoHiTech LUBRICATION certified engineers with expertise in centralized grease distribution systems. its comprehensive lubrication solutions and quality-controlled manufacturing processes ensure optimal system performance and long-term reliability.A bearing failure in a steel mill rolling stand costs $127,000 in lost production per eight-hour shift. Improper progressive vs single-line grease distribution selection accounts for 34% of premature bearing failures in industrial equipment. This technical analysis provides engineering specifications and performance data for centralized lubrication system selection.
Understanding Centralized Grease Distribution Systems
Centralized lubrication systems automatically distribute measured quantities of grease to multiple lubrication points from a central reservoir. These systems comply with DIN 3404 standards for automatic lubrication systems and eliminate manual lubrication procedures while ensuring consistent equipment protection.
Industrial applications requiring centralized grease distribution include:
Manufacturing equipment with 5-100+ lubrication points
Mobile machinery operating in contaminated environments
Process equipment requiring 99%+ availability ratings
Heavy industrial machinery where bearing failure costs exceed $25,000 per incident
Three primary grease distribution technologies dominate industrial applications: Progressive, Single-Line, and Dual-Line systems. Each employs distinct mechanical principles for grease delivery, making system selection critical for operational success.
Technical Overview of Distribution Systems
Progressive Grease Distribution Systems
Progressive systems deliver grease sequentially through metering valves arranged in series. Each valve in the progressive distributor block dispenses a predetermined volume before advancing to the next valve in sequence. Operating Principle: The system operates in defined cycles. Pressurized grease flows through the first metering valve, which opens, delivers its programmed volume, then closes. Pressure then advances to the second valve, continuing sequentially until all valves complete their cycle. End-of-line feedback confirms cycle completion. Key Components:
Progressive distributor blocks with precision metering valves
Primary supply line from central pump unit
Secondary lines to individual lubrication points
End-of-line indicator for cycle monitoring
Single-Line Grease Distribution Systems
Single-Line systems distribute grease simultaneously to all lubrication points through parallel injectors. When the pump pressurizes the main line, all injectors activate concurrently. Operating Principle: System operation consists of two phases: pressurization and venting. During pressurization, all injectors receive grease simultaneously through the main supply line. The venting phase depressurizes the system, allowing injector pistons to reset for the next cycle. System Configurations:
Single-Line Parallel: Direct parallel connection of all injectors
Single-Line Resistance: Flow restrictors control individual grease volumes
Single-Line Progressive: Hybrid approach combining parallel and sequential elements
Dual-Line Grease Distribution Systems
Dual-Line systems employ two main supply lines operating in alternating cycles. A reversing valve switches pressure between lines A and B, feeding distributor blocks connected to both lines. Operating Principle: The system alternates pressure between two main lines. While line A supplies pressurized grease, line B remains vented. The reversing valve then switches states, pressurizing line B while venting line A. This alternating action drives distributor blocks connected to both lines. System Architecture:
Two parallel main supply lines
Reversing valve with pneumatic or electric actuation
Distributor blocks connected to both supply lines
Individual metering units at each lubrication point
Comprehensive System Comparison
Specification
Progressive
Single-Line
Dual-Line
Working Principle
Sequential valve operation
Simultaneous parallel distribution
Alternating dual-line supply
Maximum Lubrication Points
Unlimited
6-12 per pump
100+ per system
Grease Delivery Accuracy
±5% (DIN 3404 compliant)
±15%
±10%
Operating Pressure Range
50-150 bar
50-100 bar
100-300 bar
Maximum Transmission Distance
100m
30m
300m+
Cycle Time
Variable (2-30 minutes)
Fixed (1-60 minutes)
Variable (5-120 minutes)
Monitoring Capability
End-of-line detection
Pressure monitoring only
Line switching confirmation
System Complexity
Moderate
Low
High
Initial Cost
Medium
Low
High
Maintenance Requirements
Moderate
Minimal
High
Environmental Rating
IP54-IP65
IP65-IP67
IP54-IP65
Technical Performance Analysis
Progressive vs Single-Line Grease Distribution: Technical Performance Analysis
Grease Distribution Control: Progressive vs single-line grease distribution systems differ fundamentally in metering control. Progressive systems deliver variable volumes through sequential metering valves, enabling customized grease delivery based on bearing load and operating conditions. Single-line systems provide uniform volumes to all points simultaneously, limiting flexibility but ensuring consistent distribution timing. Monitoring and Diagnostics: Progressive grease distribution offers end-of-line detection and cycle completion monitoring. Single-line grease distribution relies on pressure monitoring without individual point status feedback. This difference impacts predictive maintenance capabilities and fault diagnosis procedures. Scalability Analysis: Progressive grease distribution scales without theoretical limits through modular distributor expansion. Single-line grease distribution faces practical limitations at 8-12 points due to pressure drop and flow distribution constraints. Applications exceeding this range require multiple single-line systems or progressive alternatives.
Progressive vs Single-Line Grease Distribution Selection Criteria
Application Size Analysis:
1-8 lubrication points: Single-line grease distribution provides optimal cost-effectiveness
8-50 lubrication points: Progressive grease distribution offers superior flexibility and monitoring
50+ lubrication points: Dual-line systems deliver maximum capacity and reliability
Environmental Factors: Progressive vs single-line grease distribution selection requires environmental analysis. Temperature extremes favor dual-line systems (-20°C to +120°C) over single-line systems (-30°C to +70°C). Progressive systems handle intermediate ranges (-20°C to +80°C). All systems require IP65+ protection in contaminated environments. Distance Requirements: Single-line grease distribution limits transmission to 30 meters due to pressure constraints. Progressive grease distribution extends range to 100 meters through higher operating pressures. Applications exceeding 100 meters require dual-line systems capable of 300+ meter transmission.
Performance Advantages and Limitations
Progressive System Analysis
Technical Advantages:
Precise metering accuracy (±5% per DIN 3404 standards)
Uniform grease distribution regardless of point requirements
Pressure drop limits transmission distance
Reduced monitoring capability for individual point diagnosis
Dual-Line System Analysis
Technical Advantages:
Maximum capacity supporting 100+ lubrication points
Extended transmission distances (300+ meters)
Robust construction for heavy industrial applications
Comprehensive monitoring through line switching confirmation
Integration with industrial automation systems
Operational Limitations:
High system complexity requiring specialized maintenance
Significant initial investment and installation costs
Higher power consumption due to dual-line operation
Extended commissioning time and startup procedures
Progressive vs Single-Line Grease Distribution Applications
Manufacturing Equipment: Progressive grease distribution systems suit CNC machining centers, packaging equipment, and automated assembly lines requiring variable grease volumes and cycle monitoring. Single-line grease distribution applies to simpler manufacturing equipment with uniform lubrication requirements and cost constraints. Mobile Equipment: Construction and agricultural machinery typically employ single-line grease distribution due to space limitations, vibration resistance, and maintenance simplicity. Progressive grease distribution applies to larger mobile equipment where monitoring capability justifies system complexity. Process Industry Implementation: Chemical processing, food production, and pharmaceutical manufacturing often specify progressive grease distribution for precise control and FDA-compliant monitoring. Single-line grease distribution serves auxiliary equipment and non-critical applications within these facilities.
Progressive vs Single-Line Grease Distribution Case Studies
Application: Large automotive stamping press with 24 lubrication points Progressive vs single-line grease distribution analysis: Variable grease requirements based on tonnage and cycle rate necessitated progressive system selection Technical Specifications:
Operating pressure: 120 bar
Cycle time: 8 minutes complete sequence
Grease type: NLGI Grade 2 lithium complex
Monitoring: End-of-line detection with PLC integration
Performance Results:
40% reduction in maintenance labor hours
25% decrease in bearing failure rates
99.2% system availability over 12-month period
ROI achievement in 14 months
Single-Line Grease Distribution: Food Processing
Application: Conveyor system with 8 identical bearing assemblies Progressive vs single-line grease distribution analysis: Uniform lubrication requirements and FDA compliance favored single-line system selection Technical Specifications:
Operating pressure: 80 bar
Cycle frequency: 30 minutes
Grease type: FDA-approved NLGI Grade 2
Environmental rating: IP67 with washdown capability
Performance Results:
70% reduction in manual lubrication time
Zero contamination incidents over 18-month period
99.8% system reliability
ROI achievement in 9 months
Common Implementation Challenges
System Sizing Errors
Problem: Undersizing system capacity for future expansion requirements Solution: Design systems for 125-150% of current lubrication point requirements
Environmental Specification Gaps
Problem: Inadequate consideration of temperature, contamination, and vibration Solution: Specify environmental ratings (IP65+ for harsh conditions) and temperature ranges per application analysis
Grease Compatibility Issues
Problem: Incompatible grease mixing or incorrect NLGI grade selection Solution: Conduct grease compatibility testing per ASTM D6185 standards and maintain detailed grease documentation
Installation Planning Deficiencies
Problem: Insufficient maintenance access or improper pipe routing Solution: Follow DIN 3404 installation guidelines ensuring 360-degree access to all distribution components
Frequently Asked Questions About progressive vs single line grease distribution
What determines progressive vs single-line grease distribution selection?
Progressive vs single-line grease distribution selection depends on lubrication point count, grease volume requirements, and monitoring needs. Progressive systems suit applications requiring variable grease volumes and individual point monitoring. Single-line systems suit applications requiring uniform distribution and minimal complexity.
How do maintenance costs compare in progressive vs single-line grease distribution?
Single-line grease distribution requires minimal maintenance due to simple injector design. Progressive grease distribution needs moderate maintenance for metering valve service and monitoring systems. Maintenance intervals: progressive systems 3-6 months, single-line systems 6-12 months.
Which grease distribution method provides superior monitoring capability?
Progressive grease distribution offers end-of-line detection, cycle completion monitoring, and individual valve status. Single-line grease distribution provides pressure monitoring without individual point feedback. Progressive systems integrate effectively with SCADA and predictive maintenance programs.
What limits the scalability of progressive vs single-line grease distribution?
Single-line grease distribution is limited to 8-12 lubrication points due to pressure drop and flow constraints. Progressive grease distribution has no theoretical limit, with capacity determined by pump flow rate and cycle time. System expansion requires pressure drop analysis and cycle time evaluation.
How do operating costs differ between progressive and single-line grease distribution?
Single-line grease distribution has lower operating costs due to minimal maintenance requirements. Progressive grease distribution has moderate operating costs offset by reduced bearing failures and precise grease control. Total ownership costs favor progressive systems in monitoring-critical applications.
Can progressive vs single-line grease distribution integrate with IoT systems?
Progressive grease distribution integrates with Industrial IoT platforms through digital protocols and 4-20mA signals for real-time monitoring. Single-line grease distribution offers basic pressure monitoring integration. Both systems support remote monitoring with appropriate sensor packages.
Technical Recommendations
Progressive vs Single-Line Grease Distribution Selection:For 1-12 lubrication points requiring uniform distribution:Single-line grease distribution provides optimal cost-effectiveness and reliability with minimal maintenance. For 10-50 lubrication points requiring variable volumes:Progressive grease distribution offers superior control, monitoring capability, and long-term value. For applications exceeding 50 lubrication points:Dual-line systems deliver maximum capacity for large-scale industrial operations.
Progressive vs single-line grease distribution analysis indicates progressive systems excel in manufacturing and process equipment requiring precise lubrication control. Single-line systems suit cost-sensitive applications with straightforward requirements. System selection requires analysis of lubrication point count, grease volume requirements, monitoring needs, and environmental conditions.
Proper progressive vs single-line grease distribution selection, installation, and maintenance ensure equipment reliability, reduced maintenance costs, and operational efficiency. Engineering consultation is recommended for applications exceeding 20 lubrication points or challenging environmental conditions.
For technical assistance with system selection and design, contact IsoHiTech LUBRICATION certified engineers with expertise in centralized grease distribution systems. its comprehensive lubrication solutions and quality-controlled manufacturing processes ensure optimal system performance and long-term reliability.
Mike Yao has engineered centralized lubrication systems since 2006 — from single-line machine-tool systems to progressive and dual-line systems for steel, mining and heavy equipment — and today leads application engineering at IsoHiTech Lubrication Systems, a manufacturer founded in 2023 based in Nanjing, China.
Related: For a focused guide on grease-based automatic systems, see our Automatic Grease Systems guide covering pump selection, progressive distributors, and centralized installations. Related: central…
A lubrication system is an engineered network that delivers precise quantities of lubricant to specific machine locations at controlled intervals. Correct system selection directly affects…
Centralized lubrication systems automatically distribute measured quantities of grease to multiple lubrication points from a central reservoir. These systems comply with DIN 3404 standards for automatic lubrication systems and eliminate manual lubrication procedures while ensuring consistent equipment protection.
Industrial applications requiring centralized grease distribution include:
Centralized lubrication systems automatically distribute measured quantities of grease to multiple lubrication points from a central reservoir. These systems comply with DIN 3404 standards for automatic lubrication systems and eliminate manual lubrication procedures while ensuring consistent equipment protection.
Industrial applications requiring centralized grease distribution include:
Progressive systems deliver grease sequentially through metering valves arranged in series. Each valve in the progressive distributor block dispenses a predetermined volume before advancing to the next valve in sequence. Operating Principle: The system operates in defined cycles. Pressurized grease flows through the first metering valve, which opens, delivers its programmed volume, then closes. Pressure then advances to the second valve, continuing sequentially until all valves complete their cycle. End-of-line feedback confirms cycle completion. Key Components:
Operating Principle: The system alternates pressure between two main lines. While line A supplies pressurized grease, line B remains vented. The reversing valve then switches states, pressurizing line B while venting line A. This alternating action drives distributor blocks connected to both lines. System Architecture:
