Sandblaster With Compressor Guide: Structure, Material Properties, and Performance Metrics

Types of Sandblasters with Compressor

A sandblaster with compressor is a powerful surface treatment tool that uses compressed air to propel abrasive media—such as sand, glass beads, or steel grit—at high velocity onto a surface. This process effectively removes rust, paint, scale, and contaminants, preparing surfaces for coating, restoration, or finishing. Integrated compressors provide consistent air pressure and volume, enabling faster and more efficient blasting compared to systems reliant on external air sources.

Based on design, operation, and application, sandblasters with compressors are categorized into four primary types, each suited to different project scales, precision levels, and operational environments:

Portable Pressurized Blast Containers

Compact and self-contained units that either include a built-in compressor or connect to an external one. These are ideal for on-site repairs, small-scale maintenance, and localized surface cleaning.

Advantages

• Highly portable and easy to transport
• Quick setup for field use
• Suitable for spot treatments and emergency repairs
• Lower pressure enhances operator safety

Limitations

• Limited blasting capacity due to small media reservoir
• Lower pressure reduces aggressiveness on tough coatings
• Not ideal for large or continuous jobs

Best for: Field maintenance, automotive touch-ups, small workshops, and DIY projects

Bucket Blast Cabinets (Suction-Type)

Also known as suction-blast cabinets, these systems use a vacuum effect to draw abrasive media from a bucket or hopper into the air stream. The compressed air pulls the media through a siphon system and out through the nozzle.

Advantages

• Affordable entry-level option
• Simple design with minimal maintenance
• Effective for light-duty cleaning and surface texturing
• Easy media changeover

Limitations

• Slower blasting speed due to lower media velocity
• Less efficient with larger or denser abrasives
• Higher air consumption for equivalent output

Best for: Hobbyists, light restoration, engraving, and minor surface imperfections

Pressure Blast Cabinets

These sealed, pressurized systems store abrasive media in a tank that is pressurized along with the air line. When triggered, the pressurized media is forced through the nozzle, delivering a more powerful and consistent blast stream than suction systems.

Advantages

• Higher blasting efficiency and speed
• Capable of handling coarse and heavy abrasives
• Consistent media flow for uniform surface finish
• Ideal for industrial and high-volume applications

Limitations

• Higher initial cost and complexity
• Requires more maintenance and safety checks
• Bulkier design limits portability

Best for: Manufacturing, heavy restoration, metal fabrication, and professional surface preparation

Automatic Sandblasters

Advanced systems designed for high-throughput or precision applications. These units feature automated nozzles or robotic arms that move across the workpiece inside a sealed chamber, ensuring consistent coverage without manual intervention.

Advantages

• High repeatability and uniform finish
• Reduces labor costs and operator fatigue
• Can handle complex geometries with programmed paths
• Improved safety with enclosed operation

Limitations

• Significant upfront investment
• Requires technical knowledge for programming
• Larger footprint and infrastructure needs

Best for: Production lines, aerospace components, automotive parts, and precision engineering

Type	Blasting Power	Portability	Best Use Case	Maintenance Level
Portable Pressurized	Moderate	Excellent	On-site repairs, small jobs	Low
Bucket Blast Cabinet	Low to Moderate	Good	Light-duty cleaning, hobby use	Low
Pressure Blast Cabinet	High	Fair	Industrial, large-scale projects	Moderate
Automatic Sandblaster	Very High	Poor	Mass production, precision work	High

Expert Tip: Always match the abrasive media to your project requirements—finer media for delicate surfaces and coarser media for heavy rust or paint removal. Using the wrong media can damage substrates or reduce efficiency, even with the most advanced sandblaster system.

Specifications and Maintenance of Sandblaster with Compressor

A sandblaster with an integrated compressor is a powerful surface preparation tool widely used in industrial cleaning, paint stripping, rust removal, and surface texturing. Understanding its key specifications ensures optimal performance for your application, while consistent maintenance enhances safety, efficiency, and equipment longevity.

Key Specifications to Consider

Compressor Capacity (CFM/LPM)

The compressor capacity—measured in Cubic Feet per Minute (CFM) or Liters per Minute (LPM)—determines how much air the system can deliver to the blasting nozzle. This is one of the most critical performance indicators, as insufficient airflow can result in inconsistent blasting, reduced efficiency, and longer job times.

For light-duty tasks like rust removal on small metal parts, a capacity of 8–12 CFM may suffice. However, heavy-duty applications such as large-scale industrial degreasing or ship hull cleaning often require 20 CFM or more. Always match the compressor output to the nozzle size and abrasive type to maintain optimal pressure and flow.

Working Pressure (PSI/Bar)

Working pressure, typically measured in pounds per square inch (PSI) or bar, directly influences the impact force of the abrasive media. Higher pressure results in faster material removal and a smoother, more uniform finish, especially on tough surfaces like concrete or thick paint layers.

Most sandblasters operate effectively between 80–120 PSI. Lower pressures (60–80 PSI) are suitable for delicate surfaces to avoid damage, while pressures above 100 PSI are preferred for aggressive cleaning. Ensure your compressor can sustain the required pressure throughout the operation without significant drop-offs.

Blast Pot Size (Capacity)

The blast pot holds the abrasive media and regulates its flow into the airstream. Its size—usually measured in pounds or kilograms—determines how long you can work continuously before needing to refill.

Smaller pots (25–50 lbs) are ideal for precision jobs or mobile operations where portability is key. Larger pots (100+ lbs) are better suited for extended industrial projects, minimizing downtime. Consider the job scope and accessibility when selecting pot capacity.

Material Compatibility & Construction

The materials used in the sandblaster’s construction affect its durability, resistance to corrosion, and compatibility with different abrasives. Units made from carbon steel are cost-effective but may rust over time, especially in humid environments.

Stainless steel models offer superior corrosion resistance and are ideal for use with aggressive media like aluminum oxide or in marine applications. Always verify that the internal components (valves, seals, hoses) are compatible with your chosen abrasive to prevent premature wear or chemical degradation.

Dust Collection System

An integrated dust collection system is essential for maintaining a safe and compliant work environment. It captures fine particulates generated during blasting, reducing airborne contaminants and protecting both operators and surrounding areas.

Common systems include bag filters, cartridge filters, or cyclonic separators. Bag filters are economical and easy to replace, while cartridge filters offer higher efficiency and longer service life. Regular maintenance of the filtration system ensures peak performance and compliance with OSHA or local environmental regulations.

Specification	Importance	Selection Tips
Compressor Capacity (CFM)	High	Match CFM to nozzle size and abrasive type; ensure sustained output under load
Working Pressure (PSI)	High	80–120 PSI for most applications; higher for tough surfaces, lower for delicate work
Blast Pot Size	Medium-High	Larger pots reduce refill frequency; choose based on job duration and mobility needs
Material Construction	Medium	Stainless steel for corrosion resistance; verify seal compatibility with abrasives
Dust Collection Efficiency	High	Use HEPA-grade filters for hazardous materials; clean or replace filters regularly

Essential Maintenance Practices

Regular Cleaning: After each use, thoroughly clean the blast pot, hoses, and nozzle to remove residual abrasive material. Accumulated grit can cause clogs, uneven blasting, and accelerated wear. Wipe down the exterior to prevent dust buildup that could affect electrical or mechanical components.

Inspection and Replacement of Consumable Parts: Nozzles, hoses, valves, and seals are subject to constant abrasion and should be inspected frequently. Replace worn nozzles promptly, as erosion increases air consumption and reduces blasting efficiency. Check hoses for cracks or bulges that could lead to dangerous ruptures.

Dust Collection System Maintenance: Empty the dust collector regularly and inspect filters for tears or clogging. Clean reusable filters according to manufacturer instructions, and replace disposable ones on schedule. A clogged system reduces suction power and increases operator exposure to harmful particles.

Lubrication of Moving Parts: Lubricate pneumatic valves, regulators, and any mechanical linkages with compressor-safe lubricants. Proper lubrication reduces friction, prevents seizing, and extends component life. Avoid over-lubrication, which can attract dust and create sludge.

Environmental Considerations: Store and operate the sandblaster in a dry, well-ventilated area. Excessive moisture can lead to rust and internal corrosion, while high dust levels may compromise the compressor intake and filtration systems. Avoid extreme temperatures that could affect seals or electronic controls.

Important: Always follow the manufacturer’s maintenance schedule and safety guidelines. Using incorrect abrasives, neglecting filter maintenance, or operating with damaged components can lead to equipment failure, reduced efficiency, or serious safety hazards. Regular upkeep not only protects your investment but also ensures consistent performance and a safer working environment.

Application Scenarios of Sandblaster with Compressor

Sandblasting systems powered by air compressors are essential tools across a wide range of industries due to their versatility, efficiency, and ability to prepare, clean, or modify surfaces with precision. By propelling abrasive media at high speed using compressed air, these systems deliver powerful results for both industrial and restoration tasks. Below are the key application areas where sandblasters with compressors play a critical role.

Restoration and Renovation

In construction and architectural restoration, sandblasting is widely used to remove layers of old paint, concrete coatings, rust, and soot without damaging the underlying structure. It’s particularly valuable in historic preservation projects where delicate materials like brick, stone, or masonry need cleaning after fire damage or long-term weathering.

• Removes char, smoke residue, and grime from fire-damaged buildings while preserving structural integrity
• Strips concrete surfaces and prepares them for resurfacing or repairs
• Ideal for restoring heritage buildings, monuments, and facades with minimal substrate damage
• Can be adjusted with finer abrasives (e.g., glass beads or walnut shells) for sensitive surfaces

Best practice: Use lower pressure settings and non-aggressive media for fragile historical materials.

Aeronautics and Automotive Engineering

In both automotive and aerospace engineering, sandblasting is crucial for surface preparation and performance enhancement. It ensures optimal adhesion for coatings, improves friction on key components, and removes corrosion or old finishes before reassembly.

• Roughens brake discs and rotors to improve grip and stopping power
• Prepares engine blocks, cylinders, and turbochargers for coating or painting
• Removes oxidation, paint, and contaminants from aircraft fuselages and engine parts
• Enhances bonding surfaces for composite materials in high-performance vehicles

Safety note: Precision blasting ensures passenger safety by maintaining component reliability under stress.

Production and Manufacturing Lines

In industrial manufacturing—especially in aerospace, automotive, and heavy machinery—sandblasting is integrated into production workflows to ensure quality control and durability of metal components.

• Removes burrs, flash, and scale from cast or machined parts
• Eliminates oxides and impurities from metal surfaces prior to welding or coating
• Improves paint and adhesive adhesion for long-lasting finishes
• Used in automated blasting systems for consistent, high-volume processing

Efficiency gain: Automated sandblasting increases throughput and reduces manual labor in production environments.

Graffiti Removal and Public Surface Cleaning

Municipalities and property managers use sandblasting—particularly soda blasting and dry ice blasting—to clean public surfaces without damaging the substrate or harming the environment.

• Removes graffiti from brick, concrete, marble, and granite without etching
• Safe for use on monuments, statues, and building facades in urban areas
• Soda blasting is non-toxic and water-soluble, ideal for sensitive locations
• Dry ice blasting leaves no residue, making it perfect for food-processing zones or electrical areas

Eco-friendly option: Non-abrasive methods like dry ice or baking soda minimize environmental impact.

Marine and Offshore Applications

The marine industry relies heavily on sandblasting for maintenance, repair, and preparation of vessels and offshore structures exposed to harsh saltwater environments.

• Removes marine biofouling, rust, and old coatings from ship hulls, propellers, and rudders
• Prepares surfaces for anti-corrosive paints and protective coatings
• Used in dry docks and offshore platforms for routine maintenance
• Essential for extending the lifespan of submarines, oil rigs, and floating structures

Durability focus: Proper surface prep through blasting significantly enhances coating longevity in corrosive marine conditions.

Alternative Blasting Media & Techniques

Depending on the application, different media can be used with a compressor-driven sandblaster to achieve specific results while minimizing damage or environmental impact.

• Silica sand: High-efficiency for heavy rust and paint removal (requires proper ventilation)
• Glass beads: Smooth finish, ideal for cosmetic restoration
• Steel shot: Used for peening and strengthening metal surfaces
• Soda (baking soda): Non-destructive, great for food equipment and delicate surfaces
• Dry ice: Sublimates on impact, no media cleanup required

Pro tip: Match the blasting media to the material and desired finish for optimal results.

Professional Insight: Always assess the substrate material, environmental conditions, and end goal before selecting the blasting method and media. For sensitive or public-facing projects, consider eco-friendly alternatives like soda or dry ice blasting. Ensure proper safety gear—respirators, goggles, and hearing protection—are used, especially in enclosed or high-dust environments.

Industry	Primary Use	Recommended Media	Key Benefit
Construction & Restoration	Surface cleaning, paint removal	Glass beads, walnut shells	Precise, non-damaging cleaning
Automotive	Brake prep, engine part finishing	Silica sand, aluminum oxide	Improved friction and adhesion
Aerospace	Coating removal, surface prep	Plastic media, steel shot	High precision, material integrity
Public Services	Graffiti removal	Soda, dry ice	Eco-friendly, no residue
Marine	Hull cleaning, corrosion removal	Steel grit, garnet	Durable, deep cleaning

Additional Considerations

• Compressor Requirements: Ensure adequate CFM (cubic feet per minute) and PSI output to match the nozzle size and media type for consistent performance.
• Ventilation and Safety: Use in well-ventilated areas or with dust extraction systems; silica dust requires OSHA-compliant respiratory protection.
• Media Recycling: Some systems allow for media recovery and reuse, reducing waste and operational costs.
• Environmental Compliance: Check local regulations on media disposal, especially for hazardous materials like lead-based paint removal.
• Automation Potential: Robotic or cabinet blasting systems increase repeatability and reduce labor in high-volume settings.

How to Choose the Right Sandblaster with Compressor: A Comprehensive Guide for Industrial Buyers

Selecting the ideal sandblaster with a compatible compressor is a critical decision for industrial operations. The right equipment enhances productivity, ensures surface quality, and reduces long-term maintenance costs. This guide outlines key factors to consider—from application needs to compressor compatibility—so you can make an informed, cost-effective purchase tailored to your specific requirements.

Important Note: Choosing mismatched sandblasting equipment and compressors can lead to poor performance, accelerated wear, and safety hazards. Always verify technical specifications and consult manufacturer guidelines before making a purchase.

Key Factors to Consider When Choosing a Sandblaster with Compressor

1. Application Requirements and Project Scope

   The nature of your blasting task is the most important factor in equipment selection. Different applications demand specific tools, abrasives, and pressure levels:

   • Paint and Coating Removal: Requires aggressive abrasives like steel grit or aluminum oxide and high-pressure systems such as pressure pot blasters.
   • Surface Preparation (e.g., rust removal, weld cleaning): Best achieved with steel shot or garnet media using siphon or pressure-fed systems.
   • Delicate Finishing (e.g., glass etching, cosmetic finishing): Use gentler media like glass beads with low-pressure suction blasters and fine nozzles.
   • Part Geometry: Complex or intricate parts may require specialized nozzles, rotary tables, or robotic arms to ensure even coverage. Consider swivel joints or extension wands for hard-to-reach areas.
   • Material Type:
     • Steel, iron, and carbon-based metals: Use durable steel sandblasting machines with robust media like steel grit or cut wire.
     • Aluminum and softer metals: Opt for non-ferrous abrasives such as aluminum oxide or plastic media to avoid embedding or warping.
     • Glass and ceramics: Require non-damaging abrasives like soda or fine glass beads.
   • Job Size and Environment:
     • Small indoor jobs (e.g., auto body work): A handheld siphon blaster with an air pistol grip is sufficient and portable.
     • Large outdoor or industrial-scale projects (e.g., bridge maintenance, shipbuilding): A high-capacity pressure pot system with a large-volume compressor is essential for efficiency.
2. Abrasive Compatibility and Media Selection

   Not all sandblasters are compatible with every type of abrasive. Matching the machine to the correct media ensures optimal performance and surface finish:

   • Common Abrasives and Their Uses:
     • Steel Grit: Ideal for aggressive cleaning and profiling of steel surfaces.
     • Aluminum Oxide: Hard, reusable abrasive suitable for deburring, cleaning, and preparing aluminum and other metals.
     • Garnet: Eco-friendly, sharp-edged abrasive used in precision blasting and marine applications.
     • Glass Beads: Provides a smooth, peened finish; commonly used in automotive and aerospace industries.
     • Plastic Media: Gentle on surfaces; perfect for paint stripping without substrate damage.
   • Media Size and Shape:
     • Coarse media (e.g., 20-40 mesh) removes material quickly but leaves a rougher finish.
     • Fine media (e.g., 80-120 mesh) provides a smoother finish, ideal for finishing work.
     • Angular abrasives cut faster; round media produce a peened surface.
   • Equipment Compatibility: Ensure the sandblaster’s hopper, nozzle, and hose are rated for the chosen abrasive type and size to prevent clogging or premature wear.
3. Compressor Pairing and Air Supply Requirements

   The compressor is the heart of any sandblasting system. An undersized compressor leads to inconsistent pressure and reduced efficiency:

   • CFM (Cubic Feet per Minute) Requirements:
     • Siphon (suction) blasters: Typically require 10–20 CFM at 90 PSI.
     • Pressure pot blasters: May require 25–100+ CFM depending on nozzle size and pressure.
   • Nozzle Size and Air Consumption:
     • A 1/4" nozzle may need ~25 CFM; a 3/8" nozzle can require over 50 CFM.
     • Always match nozzle size to your compressor’s output to avoid pressure drop.
   • Pressure (PSI): Most sandblasting operates between 80–100 PSI. Higher pressures (up to 120 PSI) increase speed but also wear.
   • Compressor Type:
     • Reciprocating (piston) compressors: Cost-effective for intermittent use.
     • Rotary screw compressors: Better for continuous, high-demand industrial applications.
   • Air Quality: Use a dryer and filter to prevent moisture and oil contamination, which can clog the system and ruin surface finishes.
4. Durability, Maintenance, and Total Cost of Ownership

   Industrial environments demand rugged, low-maintenance equipment. Consider long-term reliability over initial cost:

   • Construction Materials: Look for units made from hardened steel, ceramic nozzles, and abrasion-resistant hoses to withstand continuous use.
   • Wear Parts: Nozzles, valves, and seals wear quickly. Choose models with easily replaceable components and available spare parts.
   • Maintenance Schedule: Regular cleaning, inspection, and lubrication extend equipment life. Some systems feature quick-disconnect fittings for easier servicing.
   • Warranty and Support: Reputable brands often offer 1–3 year warranties and technical support, reducing downtime and repair costs.
   • Total Cost of Ownership: Factor in energy consumption, media efficiency, and expected lifespan when comparing options.

Blasting Method	Best For	CFM Requirement	Compressor Recommendation	Media Compatibility
Siphon (Suction) Blaster	Small jobs, light-duty use, indoor workshops	10–20 CFM @ 90 PSI	5–7 HP reciprocating compressor	Glass beads, plastic, fine garnet
Pressure Pot Blaster	Heavy-duty, large-scale, outdoor projects	25–100+ CFM @ 90–100 PSI	10+ HP rotary screw or large piston compressor	Steel grit, aluminum oxide, coarse garnet
Wet Blaster (Slurry)	Dust-sensitive environments, delicate surfaces	15–30 CFM @ 80 PSI	6–8 HP compressor with air dryer	Soda, fine sand, eco-friendly media

Expert Tip: Always perform a test blast on a scrap piece using your chosen abrasive and settings. This helps fine-tune pressure, distance, and technique before starting on the actual workpiece, ensuring consistent results and avoiding damage.

Final Recommendations for Industrial Buyers

• Research reputable brands such as Graco, Clemco, Wheelabrator, and SBP, known for durability and technical support.
• Read customer reviews and case studies to understand real-world performance and reliability.
• Consult with equipment suppliers or blasting experts to match your application with the right system.
• Consider renting or demoing equipment before making a large investment.
• Invest in proper PPE (respirators, blast suits, hearing protection) and containment systems to meet OSHA and environmental standards.

Choosing the right sandblaster and compressor combination is more than just matching specs—it’s about aligning equipment with your operational goals. By carefully evaluating your application, media needs, air supply, and long-term maintenance, you can select a system that delivers consistent, high-quality results while maximizing efficiency and safety.

Sandblaster with Compressor: Frequently Asked Questions

Q1: Can a portable sandblaster be used without a compressor?

No, a standard portable sandblaster cannot operate without a source of pressurized air. The compressor is essential for propelling abrasive media at high speed onto surfaces for effective cleaning, rust removal, or surface preparation.

However, some compact or handheld units come with built-in manual pumps or small electric air systems that allow limited operation without an external compressor. These are typically suited for light-duty tasks and use less aggressive media like baking soda or fine plastic beads. For consistent performance and industrial applications, a reliable air compressor with sufficient CFM (cubic feet per minute) and PSI (pounds per square inch) output is required.

Q2: Can users build their own sandblaster with a compressor?

While some DIY enthusiasts attempt to construct homemade sandblasters using components like spray guns, pressure containers, or shop vacuums, this approach is strongly discouraged due to significant safety and performance risks.

• Safety Hazards: Homemade units often lack proper pressure regulation, leading to potential ruptures, explosions, or uncontrolled media discharge.
• Ineffectiveness: Without precision nozzles and sealed chambers, DIY sandblasters fail to generate consistent pressure or accurate media flow, resulting in poor blasting efficiency.
• Material Compatibility: Improper materials (e.g., PVC pipes) can degrade under pressure and abrasive wear, increasing the risk of shrapnel and injury.
• Lack of Controls: Commercial units include safety valves, pressure gauges, and ergonomic triggers—features rarely replicated in DIY versions.

For reliable, safe, and efficient results, it's best to invest in a professionally manufactured sandblasting system designed to meet industry standards.

Q3: What are the safety requirements for using a sandblaster with a compressor?

Sandblasting generates hazardous dust, noise, and flying debris, making comprehensive personal protective equipment (PPE) essential for operator safety. Key safety measures include:

• Respiratory Protection: A full-face respirator with P100 filters or a powered air-purifying respirator (PAPR) is critical—especially when blasting materials containing silica, which can cause silicosis if inhaled.
• Eyewear: Anti-fog, impact-resistant safety goggles or face shields should be worn even under a helmet.
• Hearing Protection: Earmuffs or earplugs are necessary due to high noise levels from the compressor and blasting nozzle.
• Protective Clothing: Flame-resistant, anti-static coveralls or sandblasting suits prevent skin exposure and reduce static buildup.
• Gloves: Heavy-duty, abrasion-resistant gloves protect hands from sharp particles and vibration.
• Sandblasting Helmet: Recommended for prolonged use; includes integrated airflow, cooling systems, and clear face shields.

In addition to PPE, always work in a well-ventilated area or within an enclosed blasting cabinet. Ensure the equipment is properly grounded to prevent static discharge, and follow OSHA or local workplace safety regulations—especially in commercial or industrial environments.

Q4: What is the difference between external and internal sandblasters with a compressor?

The distinction between external and internal sandblasters lies in their application, design, and method of media delivery:

Feature	External Sandblaster	Internal Sandblaster
Primary Use	Surface cleaning, paint stripping, rust removal on exterior surfaces (e.g., metal frames, machinery, vehicles).	Cleaning or preparing the interior of pipes, tubes, tanks, or confined spaces.
Design	Bulkier setup with a pressurized pot, long hoses, and large nozzles; often mounted on carts or stands.	Compact, flexible nozzles or lance-style tools designed to fit inside narrow openings.
Media Flow	Uses siphon or pressure-fed systems to deliver abrasive media over long distances.	Employs specialized feed mechanisms with filters or cyclonic separators to manage debris and prevent clogging.
Safety & Containment	Requires full PPE and containment barriers to control dust and rebounding particles.	Often used with vacuum-assisted systems to capture spent media and dust from enclosed areas.
Typical Applications	Auto body shops, construction, metal fabrication.	Pipe maintenance, HVAC systems, industrial plumbing.

Choosing the right type depends on your project scope—external systems offer power and coverage, while internal models provide precision and access to hard-to-reach areas.

Q5: Can I buy a sandblaster with compressor in bulk from Alibaba.com?

Yes, Alibaba.com offers a wide range of sandblasting equipment available for wholesale purchase, including complete sandblaster-compressor kits, standalone units, replacement parts, and accessories.

• Variety: Options include siphon-feed, pressure-feed, and wet blasting systems compatible with various compressors.
• Customization: Many suppliers offer OEM/ODM services, allowing businesses to brand equipment or tailor specifications.
• Volume Pricing: Bulk orders typically come with discounted rates, making it cost-effective for distributors, workshops, or contractors.
• Global Shipping: Most vendors support international logistics and can provide certifications (CE, ISO) upon request.

When purchasing in bulk, verify supplier credentials, read customer reviews, and request product specifications to ensure compatibility with your intended use. It’s also advisable to order a sample first to evaluate build quality and performance before committing to large quantities.