Exploring Elevator Hydraulic Buffer: Technical Specifications, Structure, and Performance Insights

Types of Elevator Hydraulic Buffers

An elevator hydraulic buffer is a critical safety device installed at the bottom of the elevator shaft to absorb and dissipate kinetic energy during unexpected descents or over-travel scenarios. These buffers play a vital role in protecting passengers, equipment, and the structural integrity of the elevator system by ensuring controlled deceleration. Different types of buffers are engineered for specific applications, speeds, and load capacities, each offering unique performance characteristics.

Terminal Hydraulic Buffers

Installed at the extreme lower ends of elevator travel, these robust buffers are designed to safely stop the elevator car or counterweight in emergency over-speed situations. They are essential in high-rise buildings where potential impact energy is significantly higher due to increased travel distance and velocity.

Advantages

• High energy absorption capacity
• Advanced hydraulic damping for smooth deceleration
• Durable construction for long-term reliability
• Compliant with stringent safety standards

Limitations

• Larger size requires more installation space
• Higher initial cost compared to simpler types
• Requires periodic maintenance and fluid checks

Best for: High-rise elevators, high-speed systems, commercial and industrial applications

Standard Hydraulic Buffers

The most widely used type in modern elevators, these buffers utilize a sealed cylinder filled with hydraulic fluid. When impacted, the piston forces fluid through calibrated orifices, converting kinetic energy into heat. This controlled fluid displacement ensures a smooth, quiet, and predictable stopping action.

Advantages

• Smooth and quiet operation
• Precise energy dissipation control
• Customizable for various load and speed ratings
• Consistent performance over time

Limitations

• Requires periodic inspection for fluid leaks
• Performance can degrade if fluid degrades or leaks
• More complex than mechanical alternatives

Best for: Mid- to high-rise residential and commercial elevators, medium-speed applications

Non-Terminal Hydraulic Buffers

Positioned at intermediate points within the elevator shaft, these buffers provide additional safety layers by mitigating impacts during abnormal operations or maintenance scenarios. Unlike terminal buffers, they are not intended for full emergency stops but enhance system resilience during unexpected movements.

Advantages

• Enhances overall system safety redundancy
• Compact design allows flexible installation
• Reduces risk during maintenance or testing
• Supports smoother operation under irregular conditions

Limitations

• Not designed for full emergency energy absorption
• Limited deployment in standard configurations
• May require custom engineering for integration

Best for: Complex elevator systems, maintenance access zones, specialized industrial elevators

Spring Buffers

Utilizing coiled steel springs, these mechanical buffers compress upon impact to absorb energy. Commonly found in low-speed elevators (typically under 0.63 m/s), they are valued for their simplicity and cost-effectiveness, though they offer less refined performance compared to hydraulic systems.

Advantages

• Low initial cost and simple design
• No fluid maintenance required
• Reliable in basic applications
• Easily replaceable components

Limitations

• Less efficient energy absorption
• Can cause abrupt or bouncy stops
• Prone to metal fatigue over time
• Performance affected by temperature and corrosion

Best for: Low-speed freight elevators, home elevators, older installations, budget-conscious projects

Magnetic (Eddy Current) Buffers

Advanced electromagnetic systems that use eddy currents generated by moving conductive plates through magnetic fields to create resistance and absorb kinetic energy. These cutting-edge buffers offer contactless operation, resulting in minimal wear and maintenance.

Advantages

• Near-zero maintenance requirements
• No physical contact or wear parts
• Precise, adjustable damping based on speed and mass
• Highly durable and long service life

Limitations

• Significantly higher initial cost
• Complex integration with control systems
• Limited availability and specialized expertise needed

Best for: High-tech buildings, smart elevators, research facilities, and premium installations

Buffer Type	Energy Efficiency	Maintenance Needs	Operating Smoothness	Recommended Use
Terminal Hydraulic	Excellent	Moderate	Excellent	High-rise, high-speed elevators
Standard Hydraulic	Very Good	Moderate	Excellent	Commercial/residential mid-rise
Non-Terminal Hydraulic	Good	Moderate	Good	Supplementary safety systems
Spring	Fair	Low	Fair	Low-speed, light-duty elevators
Magnetic	Excellent	Very Low	Excellent	High-tech, smart building systems

Expert Tip: Regular inspection and maintenance of hydraulic buffers—including checking fluid levels, seals, and piston movement—are essential to ensure optimal performance and compliance with safety codes. For spring buffers, look for signs of corrosion or permanent deformation, which can compromise safety.

Functions and Features of Elevator Hydraulic Buffer

Elevator hydraulic buffers are essential safety components designed to protect both passengers and equipment in the event of an over-travel or emergency descent. Installed at the bottom of elevator shafts, these devices absorb kinetic energy from the elevator car or counterweight, ensuring a controlled and gradual stop. As a critical part of modern elevator safety systems, hydraulic buffers combine mechanical precision with fluid dynamics to deliver reliable performance under extreme conditions.

Core Functions of Hydraulic Buffers

Shock Absorption

Hydraulic buffers are engineered to absorb and dissipate the kinetic energy generated when an elevator car or counterweight reaches the end of its travel path unexpectedly. This function is vital for preventing sudden deceleration that could result in injury or structural damage. By converting motion energy into heat through fluid displacement, hydraulic buffers ensure a smooth and controlled stop.

Advancements in hydraulic elevator technology have significantly improved the responsiveness and efficiency of these buffers. Their consistent performance under various load conditions makes them ideal for both low- and mid-rise buildings, offering a reliable solution for safe elevator operation.

Compression and Expansion

During impact, the hydraulic buffer undergoes a controlled compression phase where the piston forces hydraulic fluid through precision orifices. This linear and fluid motion allows for gradual deceleration rather than abrupt halting. As the force diminishes, the system may expand back to its original position, ready for subsequent use.

The design ensures consistent resistance throughout the stroke, minimizing jarring movements and enhancing passenger comfort. This predictable behavior is especially important during emergency scenarios, where stability and control are paramount.

Damping Effect

The hydraulic fluid within the buffer acts as a damping medium, resisting flow during compression. This resistance converts kinetic energy into hydraulic energy and ultimately into heat, which is safely dissipated. The damping mechanism ensures a smooth, progressive slowdown of the elevator car or counterweight.

In addition to improving ride quality, this feature reduces vibrations and operational noise during deceleration. Over time, effective damping also decreases mechanical stress on guide rails, suspension ropes, and other critical components, contributing to the overall longevity and reliability of the elevator system.

Buffering Capacity

Hydraulic buffers are designed to accommodate a wide range of elevator loads and travel speeds. Their adjustable or scalable stroke lengths allow customization based on building height, car weight, and speed ratings. This adaptability makes them suitable for diverse applications—from residential buildings to commercial high-rises.

Advanced models feature enhanced buffering capacity, enabling safe deceleration even during overloading conditions or unexpected free-fall scenarios. Engineers select buffer specifications based on safety codes (such as ASME A17.1 or EN 81), ensuring compliance and optimal protection.

Key Features Enhancing Performance and Safety

Durability and Reliability: Constructed from high-grade steel and corrosion-resistant materials, hydraulic buffers endure repeated compression cycles without degradation. Internal components are lubricated with specialized hydraulic oil, reducing friction and wear. Rigorous testing, including drop tests and fatigue analysis, verifies long-term reliability and compliance with international safety standards.

Low Maintenance Requirements: One of the major advantages of hydraulic buffers is their minimal maintenance needs. After installation, routine servicing typically involves only periodic inspection and scheduled replacement of hydraulic fluid every 3–5 years, depending on usage. This reduces downtime and operational costs while maintaining peak performance.

Self-Resetting Mechanism: Unlike spring-based buffers, most hydraulic buffers automatically return to their original position after activation, eliminating the need for manual resetting. This self-recovering feature ensures continuous readiness for multiple impact events, enhancing overall system safety.

Leak-Proof Sealing: Modern hydraulic buffers utilize advanced sealing technologies to prevent fluid leakage, even under high pressure and temperature fluctuations. This maintains consistent damping performance and prevents environmental contamination.

Temperature Stability: High-quality hydraulic fluids are formulated to maintain viscosity across a broad temperature range, ensuring reliable operation in varying climatic conditions—from cold basements to hot machine rooms.

Feature	Function	Benefit
Hydraulic Damping	Converts kinetic energy into heat via fluid resistance	Smooth deceleration, reduced noise, and vibration
Adjustable Stroke Length	Customizable compression distance based on elevator specs	Adaptable to different building heights and speeds
High Load Tolerance	Supports operation under normal and overload conditions	Enhanced safety during emergencies or overcapacity
Sealed Fluid System	Prevents oil leakage and contamination	Long service life and low maintenance
Self-Resetting Design	Automatically returns to original position post-impact	Immediate readiness for repeated use without intervention

Important: Hydraulic buffers must be inspected annually by certified technicians and tested according to local elevator safety regulations. Any signs of fluid leakage, corrosion, or inconsistent performance should prompt immediate service. Using non-approved fluids or delaying maintenance can compromise safety and lead to buffer failure. Proper care ensures continued protection for passengers and compliance with legal requirements.

Applications of Elevator Hydraulic Buffers

Elevator hydraulic buffers play a vital role in ensuring the safety, comfort, and longevity of vertical transportation systems. As a critical component in both passenger and freight elevators, these devices absorb kinetic energy during unexpected over-speed conditions or at the terminal landing, providing controlled deceleration and minimizing impact forces. Their reliability and efficiency make them indispensable across a wide range of industries and building types worldwide.

With increasing demands for occupant safety and smooth ride quality, hydraulic buffers have become standard in modern elevator installations. Below are the primary applications where hydraulic buffers deliver essential performance benefits.

Commercial Buildings

Office complexes, shopping malls, hotels, and hospitality centers rely heavily on elevators to move large volumes of people and goods daily. Hydraulic buffers are integrated into both passenger and service elevators to ensure safe, smooth stops—even under peak load conditions.

• Support high-traffic operations with consistent performance
• Enable quiet and vibration-free deceleration, enhancing user comfort
• Handle variable loads from luggage, catering carts, and maintenance equipment

Key Benefit: Improved ride quality and reduced mechanical stress in high-use environments

Residential Buildings

From private homes to high-rise condominiums, residential elevators require dependable safety mechanisms. Hydraulic buffers are especially valuable in multi-story and luxury residences where smooth operation and noise reduction are priorities.

• Ensure gentle stopping even with heavy furniture or mobility devices
• Minimize noise and jolts, contributing to a premium living experience
• Ideal for home elevators with limited space and weight-sensitive designs

Design Advantage: Compact integration with hydraulic elevator systems commonly used in homes

Healthcare Facilities

Hospitals, clinics, and long-term care centers depend on elevators to transport patients, medical staff, and sensitive equipment. Safety and stability are paramount—especially when moving patients on stretchers or life-support systems.

• Provide controlled deceleration to prevent patient discomfort or injury
• Withstand frequent use and heavy-duty cycles in emergency and routine transport
• Meet strict regulatory standards for medical facility safety compliance

Critical Need: Zero-jerk stops essential for patient well-being and equipment integrity

Manufacturing & Industrial Plants

Factories and production facilities use freight elevators to move raw materials, machinery, and finished goods. These environments demand robust components capable of withstanding heavy loads and continuous operation.

• Absorb high-impact energy from dense industrial payloads
• Reduce wear on guide rails, car frames, and hoisting mechanisms
• Extend maintenance intervals and lower lifecycle costs

Durability Focus: Resistant to dust, vibration, and temperature fluctuations common in industrial settings

Warehouses & Logistics Centers

In distribution hubs and automated storage systems, elevators move inventory between levels with precision. Hydraulic buffers ensure reliable terminal stopping, preventing damage to goods and infrastructure.

• Facilitate seamless integration with automated material handling systems
• Prevent cargo shifting or toppling during deceleration
• Maintain operational efficiency in fast-paced logistics environments

Operational Impact: Minimizes downtime and product damage in high-throughput operations

Airports & Transportation Hubs

Airports utilize elevators in passenger terminals, baggage handling systems, and cargo loading zones. These systems operate continuously and must meet rigorous safety and reliability standards.

• Ensure safe movement of luggage, passengers, and ground support equipment
• Support 24/7 operations with minimal maintenance requirements
• Comply with aviation safety regulations and building codes

Safety Priority: Essential for protecting both people and high-value cargo in complex terminal layouts

Parking Garages

Automated vehicle lifts and multi-level parking systems use hydraulic elevators to transport cars vertically. Given the weight and value of vehicles, smooth and secure operation is critical.

• Provide precise stopping control to align vehicle platforms accurately
• Protect vehicles from jolts or misalignment during transfer
• Suitable for both indoor and outdoor installations with weather-resistant models

User Confidence: Drivers trust the system when stops are smooth and predictable

Construction Sites

Temporary personnel and material hoists are widely used during building construction. These elevators face harsh conditions and variable loads, making safety components like hydraulic buffers essential.

• Adapt to changing heights and load profiles as structures rise
• Withstand exposure to dust, moisture, and extreme temperatures
• Meet OSHA and local safety codes for temporary work platforms

Risk Reduction: Prevents accidents during final approach and landing in dynamic site conditions

Entertainment Venues

Theaters, stadiums, and concert halls use elevators for stage machinery, performer access, and audience movement. Smooth, silent operation is crucial for both safety and performance integrity.

• Enable silent stage transitions and set changes without disrupting events
• Support heavy stage equipment and mobile platforms
• Integrate with building management systems for synchronized control

Performance Integration: Critical for behind-the-scenes operations in live entertainment

Educational Institutions

Universities, colleges, and schools with multi-story buildings use elevators to accommodate students, faculty, and equipment. Accessibility and safety are key concerns, especially during class changes.

• Ensure safe transport for individuals with mobility challenges
• Handle heavy loads like lab equipment, musical instruments, and library materials
• Support long-term durability with minimal maintenance

Accessibility Compliance: Supports ADA and universal design standards in campus infrastructure

Engineering Insight: Hydraulic buffers are preferred in low- to mid-rise buildings (up to 6–7 floors) where hydraulic elevators are commonly used. They offer superior energy absorption, require less headroom than spring buffers, and provide a more controlled response under overload conditions. For optimal performance, regular inspection and fluid maintenance are recommended to ensure consistent damping characteristics over time.

Application Sector	Primary Use Case	Load Range	Key Buffer Requirement
Commercial Buildings	Passenger & freight transport	1,000–5,000 lbs	Smooth deceleration, low noise
Healthcare Facilities	Patient & equipment transport	1,500–6,000 lbs	Gentle stops, high reliability
Manufacturing Plants	Heavy machinery movement	5,000–20,000+ lbs	High impact resistance, durability
Warehouses	Inventory & pallet transport	3,000–15,000 lbs	Precise alignment, wear resistance
Airports	Baggage & passenger lifts	2,000–8,000 lbs	Continuous operation, safety compliance
Parking Garages	Vehicle vertical transport	5,000–10,000 lbs (per car)	Accurate positioning, stability

Additional Considerations

• Regulatory Compliance: Hydraulic buffers must meet international safety standards such as EN 81-2, ASME A17.1, and ISO 4190
• Maintenance Needs: Require periodic fluid checks and seal inspections to maintain optimal performance
• Environmental Options: Biodegradable hydraulic fluids available for eco-sensitive installations
• Customization: Available in various stroke lengths and mounting configurations for retrofit or new installations
• Lifespan: Properly maintained units can last 15–20 years, offering excellent long-term value

How to Choose the Right Elevator Hydraulic Buffer

Selecting the appropriate hydraulic buffer is essential for ensuring the safety, reliability, and longevity of an elevator system. Hydraulic buffers play a critical role in absorbing kinetic energy during overtravel scenarios—when an elevator car or counterweight moves beyond its normal limits. Proper selection prevents equipment damage and protects passengers. This comprehensive guide outlines the key factors to consider when choosing a hydraulic buffer, helping engineers, technicians, and building managers make informed decisions that comply with safety standards and performance requirements.

Safety Warning: Always ensure that hydraulic buffers are selected and installed in accordance with local building codes, ASME A17.1/CSA B44 safety standards, and manufacturer specifications. Improper buffer selection or installation can result in catastrophic failure during emergency stops.

Key Factors in Hydraulic Buffer Selection

1. Capacity (Load Rating)

   Hydraulic buffers are engineered to absorb energy based on the mass and speed of the elevator car or counterweight. The buffer's rated capacity must match or exceed the total weight it is designed to stop, including the car, passengers, and any additional load.

   • Determine the maximum rated load of the elevator (e.g., 1000 kg, 2000 lbs)
   • Account for the tare weight (empty car weight) when calculating total mass
   • Select a buffer with a capacity that meets or exceeds the combined load
   • Overloading a buffer can lead to bottoming out, structural damage, or failure to decelerate safely
   • Under-sizing compromises passenger safety and may violate regulatory codes
2. Travel Distance (Buffer Stroke)

   The travel distance, or stroke length, refers to how far the plunger can extend into the cylinder during compression. This must align with the available space in the elevator pit and the expected stopping distance under emergency conditions.

   • Short-stroke buffers (e.g., 50–100 mm) are suitable for low-speed elevators (≤1.0 m/s)
   • Long-stroke buffers (e.g., 150–500 mm) are required for higher-speed elevators to allow gradual deceleration
   • Insufficient stroke may result in abrupt stops, increasing injury risk and equipment stress
   • Excessive stroke wastes space and increases installation complexity
   • Consult the elevator’s speed and deceleration profile to determine required stroke
3. Installation Requirements and Space Constraints

   Proper installation is crucial for optimal buffer performance. The physical and technical environment of the elevator pit must be evaluated before selection.

   • Measure available pit depth to ensure adequate clearance for full buffer compression
   • Verify mounting configuration (bolt-down, threaded stud, or flange mount)
   • Ensure proper alignment with the bumper block on the elevator car or counterweight
   • Check for accessibility for maintenance, fluid inspection, and replacement
   • Consider environmental factors such as moisture, temperature, and potential exposure to debris
   • Some models require oil reservoirs or venting—ensure space and orientation accommodate these needs
4. Quality, Certification, and Compliance

   The reliability of a hydraulic buffer depends heavily on manufacturing quality and adherence to international safety standards.

   • Choose buffers certified to recognized standards such as ASME A17.1, EN 81-20, ISO 9001, or CE marking
   • Look for third-party testing documentation verifying performance under rated conditions
   • Premium materials (e.g., corrosion-resistant steel, high-grade seals) enhance durability and reduce maintenance
   • Avoid non-certified or generic buffers, which may not perform reliably in emergency situations
   • Ensure the manufacturer provides technical support, installation guidelines, and warranty coverage

Selection Factor	Recommended Practice	Risks of Poor Selection	Verification Method
Capacity	Select buffer rated ≥ total mass (car + max load)	Buffer failure, unsafe deceleration	Compare specs with elevator load data
Travel Distance	Match stroke to elevator speed and pit depth	Harsh impact, equipment damage	Review speed/stroke charts from manufacturer
Installation	Ensure proper alignment and mounting space	Leakage, misalignment, reduced effectiveness	On-site measurement and layout check
Quality & Certification	Use only certified, tested buffers from reputable suppliers	Safety violations, liability exposure	Review certification documents and test reports

Expert Tip: Always perform periodic inspections of hydraulic buffers—at least annually or as required by local regulations. Check for oil leaks, plunger corrosion, proper fluid level, and signs of unintended activation. Rebuild or replace buffers according to the manufacturer’s recommended service interval to maintain peak performance.

Additional Considerations

• Speed Compatibility: Hydraulic buffers are typically used for elevators with speeds up to 1.0 m/s (200 ft/min). For higher speeds, consult engineering standards—some applications may require special designs or alternative buffer types.
• Maintenance Access: Choose models with accessible oil fill ports and bleed valves to simplify servicing.
• Environmental Impact: Use biodegradable hydraulic fluid where environmentally sensitive installations exist (e.g., near water sources or in green buildings).
• Redundancy: In larger elevator systems, multiple buffers may be installed to distribute load and increase safety margins.
• Documentation: Keep detailed records of buffer model, serial number, installation date, and maintenance history for compliance audits.

Choosing the right hydraulic buffer is not just a technical decision—it's a critical safety requirement. By carefully evaluating load capacity, travel distance, installation conditions, and product certification, you ensure that your elevator system remains safe, compliant, and reliable throughout its operational life. When in doubt, consult with a qualified elevator engineer or the buffer manufacturer’s technical team to confirm compatibility and optimal performance.

Elevator Hydraulic Buffer: Frequently Asked Questions

Q: What is the difference between a buffer and a piston?

In elevator systems, the terms "buffer" and "piston" refer to entirely different components serving distinct safety and operational functions:

• Hydraulic Buffer: Installed at the bottom of the elevator shaft beneath both the car and counterweight, its primary role is safety. It absorbs kinetic energy during an over-travel scenario—when the elevator descends beyond its normal limit—by compressing hydraulic fluid to decelerate the load smoothly and prevent impact damage.
• Hydraulic Piston: A key part of the elevator’s lifting mechanism in hydraulic elevators. The piston extends from a cylinder filled with hydraulic fluid and pushes the elevator car upward. When retracted, it allows the car to descend under controlled conditions via valve regulation.

While both involve hydraulics, the buffer is a passive safety device used only in emergencies, whereas the piston is an active component responsible for regular elevator movement.

Q: How does one test a hydraulic buffer?

Testing a hydraulic buffer ensures it can safely absorb impact energy during an emergency. The standard testing method follows regulated procedures:

• DROP TEST: A calibrated weight (simulating the mass of the elevator car or counterweight) is dropped from a specified height onto the buffer. This simulates real-world over-speed or over-travel conditions.
• Deceleration Measurement: Sensors record the rate at which the weight slows upon impact. Acceptable deceleration levels are defined by safety codes (e.g., ASME A17.1 or EN 81) to ensure passenger safety—typically not exceeding 9.81 m/s² (1g) average with peak limits.
• Rebound and Recovery: After compression, the buffer should return to its original position without leakage or permanent deformation.
• Frequency: Buffers are typically tested during initial installation, after maintenance or replacement, and periodically as part of statutory inspections (often every 5 years).

Only certified technicians should perform these tests using proper safety protocols and equipment.

Q: What are the common maintenance practices for hydraulic buffers?

To ensure long-term reliability and compliance with safety standards, hydraulic buffers require consistent maintenance, including:

• Visual Inspections: Check for oil leaks, corrosion, dents, or misalignment. Any visible damage may compromise performance.
• Fluid Level and Quality: Ensure the hydraulic fluid is at the correct level and free from contamination. Degraded or low fluid reduces damping efficiency.
• Functionality Testing: Periodic operational checks (including partial stroke tests where applicable) help verify smooth action and full return capability.
• Seal Integrity: Worn seals can lead to fluid leakage or air ingress, affecting performance. Replace if necessary.
• Documentation: Maintain logs of all inspections, tests, and repairs to comply with regulatory requirements and track service history.

Most building codes require professional inspection at least annually, with more frequent checks in high-traffic or industrial environments.

Q: What are the limitations of hydraulic buffers?

While highly effective, hydraulic buffers have several important limitations that must be considered in elevator design and maintenance:

• Non-Reusable After Major Impact: Following a significant activation (such as an over-speed event), the internal components may be damaged or compromised. Most hydraulic buffers must be replaced or professionally rebuilt after such incidents.
• Temperature Sensitivity: Hydraulic fluid viscosity changes with temperature, potentially affecting performance in extreme climates unless compensated for in design.
• Leakage Risk: Over time, seals can degrade, leading to fluid leakage, reduced effectiveness, and environmental concerns.
• Maintenance Intensity: Compared to simpler spring buffers, hydraulic types require more frequent checks and specialized servicing.
• Space Requirements: They often require more vertical clearance in the pit due to their stroke length and mounting configuration.

Despite these drawbacks, they remain preferred for mid- to high-speed elevators due to their superior energy absorption and smoother deceleration profile.

Q: Are there alternatives to hydraulic buffers?

Yes, several alternative buffer types exist, each suited to different elevator speeds, loads, and applications:

Buffer Type	Operating Principle	Typical Use Case	Advantages	Limitations
Hydraulic Buffer	Uses fluid displacement to absorb energy	Elevators above 1 m/s (low to high speed)	Smooth deceleration, high energy capacity	Requires maintenance, not reusable after impact
Spring Buffer	Compresses metal springs to absorb impact	Low-speed elevators (<0.63 m/s)	Simple, low cost, minimal maintenance	Rougher ride, limited energy absorption
Elastic (Polyurethane) Buffer	Deforms elastomeric material under load	Very low-speed lifts, residential elevators	Compact, quiet, no fluid leaks	Wears over time, limited durability
Pneumatic Buffer	Uses compressed air for cushioning	Specialized industrial applications	Adjustable damping, clean operation	Complex, expensive, rare in elevators

The selection depends on factors such as elevator speed, load capacity, pit depth, environmental conditions, and local safety regulations. Most modern installations use either hydraulic or spring buffers, with hydraulic being standard for commercial and high-rise buildings.