Falling Stream Sampling Systems

McLanahan Falling Stream Sampling Systems

Representative Sampling from a Falling Material Stream

McLanahan Falling Stream Sampling Systems are designed to automatically collect representative samples from bulk material as it moves through a falling or free-flowing stream.

Falling Stream Sampling is widely used in mining, minerals processing, coal, aggregates and other bulk-material applications where accurate and repeatable sampling is required.

The sampler passes through the complete falling stream and collects a defined increment of material. By sampling across the entire stream, the system helps reduce sampling bias caused by particle segregation and variations in material size, density or composition.

How Falling Stream Sampling Systems Work

A Falling Stream Sampler is installed at a suitable material transfer point, chute or discharge location where the material forms a falling stream.

During a sampling cycle, the sampler moves through the entire cross-section of the falling material stream and collects a representative increment.

After the sampling pass is completed, the collected material is transferred to the sample preparation system.

A typical sampling arrangement can be:

Bulk Material Stream → Falling Stream Sampler → Secondary Sampling → Crushing → Sample Division → Final Sample

The actual configuration depends on the material characteristics, process capacity, particle size and laboratory requirements.

Full-Stream Sampling

The key principle of Falling Stream Sampling is to collect material from the complete falling stream.

Material flowing through a transfer point can naturally segregate according to:

Particle size
Density
Shape
Moisture
Material composition

If a sample is collected from only one part of the stream, it may not accurately represent the complete material flow.

A properly designed Falling Stream Sampler cuts across the complete stream, helping ensure that coarse, fine and intermediate particles have an appropriate opportunity to be included in the sample.

Representative Sampling

Representative sampling is essential when laboratory analysis is used to evaluate the quality or composition of a bulk material.

Falling Stream Sampling can help minimize sampling errors associated with:

Particle segregation
Variable particle size
Variable density
Uneven material distribution
Changes in material composition
Manual sampling

The sampler should be designed according to the material characteristics and the required sampling accuracy.

Sampling at Transfer Points

Falling Stream Sampling is particularly suitable for material transfer points where the bulk material is already moving vertically or falling under gravity.

Potential sampling locations include:

Conveyor discharge points
Transfer chutes
Crusher discharge
Screen discharge
Material transfer towers
Stockpile feed systems
Process plant transfer points

Installing the sampler at a suitable transfer point can provide access to the complete material stream without requiring the conveyor belt to be stopped.

Automatic Sampling

Falling Stream Sampling Systems can be automated to collect increments at predetermined intervals.

The sampling system can be integrated with the plant control system and programmed according to the required sampling schedule.

Sampling can be initiated based on:

Time
Tonnage
Production quantity
Batch
Process conditions

Automated sampling helps provide consistent sampling frequency and reduces dependence on manual sampling.

Primary Sampling

The Falling Stream Sampler typically performs the primary sampling function.

The sampler extracts an increment directly from the main falling stream.

The primary sample should be sufficiently representative of the complete material stream because errors introduced during primary sampling can affect all subsequent sample preparation stages.

Secondary Sampling

Where the primary sample is larger than the quantity required for laboratory analysis, a secondary sampling stage can be incorporated.

The Secondary Sampler reduces the sample quantity while maintaining representative material characteristics.

Multiple sampling stages may be used when a high-capacity bulk material stream needs to be reduced to a relatively small laboratory sample.

Sample Crushing

Depending on the application, the collected sample may need to be reduced in particle size.

A crusher can be incorporated into the sample preparation system to reduce the material to the required size before further sample division.

Crusher selection depends on:

Maximum feed particle size
Material hardness
Material abrasiveness
Required product size
Sample capacity

Sample Division

Following crushing or size reduction, a Sample Divider can be used to produce smaller representative samples.

Proper sample division is essential to maintain the representativeness of the final laboratory sample.

The divider is selected according to the material characteristics, particle size and required sample mass.

Sampling Frequency and Increment Size

Sampling frequency and increment size should be determined according to the variability of the material and the required analytical accuracy.

Important considerations include:

Production rate
Material variability
Particle size
Bulk density
Required sample mass
Required final sample size
Laboratory requirements
Sampling objectives

A sampling program should provide sufficient increments to represent changes in the material over the required production period.

Applications

McLanahan Falling Stream Sampling Systems can be used in:

Mining
Mineral processing
Coal processing
Aggregates
Industrial minerals
Bulk material handling
Mineral laboratories
Quality control
Process monitoring
Production accounting
Metallurgical accounting
Material characterization
Continuous process sampling

Typical Materials

Falling Stream Sampling Systems can be configured for a wide range of bulk materials, including:

Ores
Coal
Aggregates
Sand
Minerals
Concentrates
Industrial minerals
Other bulk solid materials

The system configuration depends on the physical and flow characteristics of the material.

Key Features & Benefits

Representative sampling from a falling material stream
Sampling across the complete stream
Automated sampling
Sampling without stopping the main conveyor
Suitable for transfer points and discharge chutes
Consistent sampling frequency
Reduced manual sampling
Improved sampling repeatability
Primary and secondary sampling options
Sample crushing options
Sample division options
Integration with plant control systems
Suitable for continuous production streams
Improved operator safety
Configurable according to material and process conditions

Falling Stream vs. Cross Belt Sampling

Both Falling Stream and Cross Belt Sampling Systems are designed to obtain representative samples, but they operate at different locations.

Falling Stream Sampling collects material while it is falling through a transfer point or chute.

Cross Belt Sampling collects material directly from the material burden on a moving conveyor belt.

The most appropriate sampling method depends on the plant layout, material flow, conveyor arrangement, available installation space and sampling requirements.

Factors Affecting System Design

The correct Falling Stream Sampling System depends on several process and material parameters, including:

Material type
Bulk density
Maximum particle size
Particle size distribution
Moisture content
Material hardness
Material abrasiveness
Material flow rate
Chute dimensions
Transfer point configuration
Falling stream dimensions
Sampling frequency
Required increment mass
Required final sample mass
Sampling location
Available installation space
Required level of automation

Designing the Right Falling Stream Sampling System

To properly design a Falling Stream Sampling System, the following information is typically required:

Material description
Bulk density
Capacity
Maximum particle size
Particle size distribution
Moisture content
Material hardness
Material abrasiveness
Chute width
Chute dimensions
Falling stream dimensions
Material flow rate
Sampling frequency
Required increment mass
Required final sample mass
Sampling location
Existing plant arrangement
Available installation space
Required level of automation
Laboratory requirements

Representative material testing may also be recommended for applications where material characteristics are variable or where high sampling accuracy is required.