Select the right closed-loop grab sampling system, and you get representative samples, safe operation, and clean lab results every time. The key is matching your system type to the physical state and chemistry of your process stream at collection conditions.
SENSOR Sampling Systems designs and manufactures closed-loop grab sampling systems across five stream categories. Each system captures a representative sample safely, contains and mitigates hazardous emissions. This guide identifies which category fits your process stream so you start with the right system type.
Start With Your Process Media Data
Before evaluating any system, gather these four data points. They determine your process media category before any other specification decision.
- Phase at collection conditions: is the sample a gas, vapor, or liquid?
- Vapor pressure at collection temperature: will it stay liquid in an open container, or flash to vapor?
- Operating pressure and temperature at the sample point.
- Physical and chemical properties: does the stream solidify when cooled, or contain H2S, HF acid, or other aggressive components?
Those four data points map to one of the five categories below. Metallurgy, connection details, pressure ratings, purge configuration, and heating requirements all follow from that classification.
The Five Process Media Categories
Gases and Vapors
Gas or vapor at collection conditions means this category. Bottle collection is not an option. The sample goes directly into a sealed, pressure-rated cylinder to preserve its phase from the process line to the lab.
SENSOR designs gases and vapors systems for zero emissions and zero operator exposure. Continuous circulation on a fast loop ensure zero dead volume and a good representative sample. Key engineering variables cover cylinder pressure rating, materials for H2S and acid gas service, and purge circuit design.
Refinery fuel gas headers, hydrogen-rich streams, and wellhead separator gas fall here. So do sales gas metering points, reactor off-gas, and polymer plant vent streams.
Liquefied Gases
Liquefied gases stay liquid only because of elevated operating pressure. Reduce that pressure, and the media flashes to vapor. Propane, butane, LPG, anhydrous ammonia, and ethylene are common examples.
Any pressure reduction during collection causes you to lose the heavier components to flash. As a result, the sample reaching the lab no longer represents the process stream.
SENSOR addresses this with cylinder systems built for liquefied gas service. Sight glasses verify cylinder outage and confirm liquid collection before cylinder disconnection. That confirmation step separates a valid sample from a failed one.
LPG fractionation units and refinery alkylation streams belong here. Natural gas liquids terminals and petrochemical ethylene and propylene product streams fall in this category as well.
Heavy Liquids
Heavy liquids carry high viscosity, high pour point, or both. Without active heating, these streams solidify in sample lines and collection containers before reaching the lab.
SENSOR heavy product liquid systems include heated sample lines, heated collection containers, and high-temperature valve packing as standard. Operating temperatures regularly exceed 500 degrees F. Some vacuum residue and pitch streams run above 650 degrees F. Standard off-the-shelf materials do not meet this service. SENSOR selects the metallurgy, seal materials, and heat management design for your actual conditions.
Vacuum tower bottoms, atmospheric residuum, and heavy gas oil fall here. Pitch and tar streams across refining and petrochemical service belong in this category as well.
Low Vapor Pressure Liquids
Low-vapor-pressure liquids remain stable at ambient pressure and temperature. They do not flash. They do not solidify at ambient conditions. In fact, this is the largest category by sampling point count in any refinery or chemical plant.
Bottle collection fits here. SENSOR uses a flow-through valve design that combines sample collection, nitrogen purge, and venting without extra manual steps. The flow through the fast loop design ensures no stagnant material is in the collection line before each sample. As a result, the bottle receives live process stream content, not dead-leg liquid. SENSOR BBSS is also designed to meet the TA LUFT requirements where emissions compliance demands it.
Naphtha, diesel, kerosene, sour water, and lube base stocks fall here. Crude unit side draws and organic solvents in chemical processing belong in this category as well.
Engineered Solutions
Some streams do not fit cleanly into any single standard category. SENSOR engineers custom closed-loop sampling systems for applications where standard configurations create safety problems, sample quality failures, or installation conflicts.
Engineered Solutions cover HF acid service requiring full Monel construction. They also address streams above 800 degrees F or below minus 50 degrees F. Pressures above 3,000 psig, toxic streams, and materials that solidify at sample conditions are also included. Multi-phase streams, confined space installations, multi-point collection panels, and reactive chemicals such as phosgene and ethylene oxide also fall here.
In each case, SENSOR engineers work outward from your conditions. They build the system design to fit your application, not the other way around.
Quick Reference: Stream Category Selection
Use this table as a starting point. Confirm your category with a SENSOR Sampling Systems applications engineer before design begins.
| Category | Stream Condition | Key Design Feature | Typical Applications | SENSOR Product |
| Gases and Vapors | Gas or vapor at collection conditions | Zero emissions, zero operator exposure | Fuel gas, hydrogen, separator gas, reactor off-gas | VSS Vapor Sampling System, DTSS Gas Sampling and Spot Testing |
| Liquefied Gases | Liquid only under pressure; flashes at ambient | Sight glass cylinder systems for outage verification | LPG, propane, butane, ammonia, ethylene, NGL products | LGSS Liquefied Gas Sampling System |
| Heavy Liquids | Solidifies or thickens at ambient temperature | Heated lines, containers, and valve trim | Vacuum tower bottoms, residuum, heavy gas oil, pitch | HPSS Heavy Products Sampling System |
| Low Vapor Pressure Liquids | Stable liquid at ambient pressure and temperature | Flow-through valve, closed-loop purge | Naphtha, diesel, kerosene, lube stocks, solvents | BBSS Basic Bottle Sampling System, PIBSS Pressure Isolating Bottle Sampling System, DHSS Diesel Hydrotreater, ISS Inline Sampling System, IVSS Inline Valve Sampling System, RSS RAM Sampling System |
| Engineered Solutions | Outside standard category parameters | Custom design for your process and site | HF acid, extreme temps, confined spaces, multi-phase | HFSS HF Acid Sampling System; custom multi-point and specialty configurations |
Why Every System Is Engineered to Order
Two plants running similar process media rarely share the same installation. Flange ratings, area classifications, emission permit limits, available utilities, and operator access all differ from site to site. Stream chemistry adds further variation. Naphtha from a straight-run unit at 80 degrees F behaves differently from naphtha off a reformer at 280 degrees F.
SENSOR engineers every system to your specific process data and site requirements. Custom drawings capture every dimension, connection, material, and pressure rating before fabrication begins. You review and approve the drawings. The system then ships ready to install.
For a detailed look at how the engineered-to-order process works, including site constraints, piping integration, and the drawing review process, read When Standard Sampling Systems Fail: How the SENSOR Sampling Systems Engineered-to-Order Approach Solves the Problem.
Step-by-Step Selection Guide
Work through these steps before contacting SENSOR Sampling Systems. The more process data you bring, the faster the application review goes.
- Step 1 — Phase at collection conditions. Gas or vapor means Gases and Vapors. Liquid continues to Step 2.
- Step 2 — Vapor pressure at ambient. Above atmospheric means Liquefied Gases. Below atmospheric continues to Step 3.
- Step 3 — Viscosity and pour point at ambient. Solidifies or thickens below 150 degrees F means Heavy Liquids. Otherwise, continue to Step 4.
- Step 4 — Specialty chemistry or installation constraints. HF acid, extreme temperatures, pressures above 3,000 psig, toxic materials, confined spaces, or multi-phase conditions mean Engineered Solutions. None of these continues to Step 5.
- Step 5 — Stable liquid at ambient with no specialty chemistry or constraints. Low Vapor Pressure Liquids apply.
Frequently Asked Questions About Closed-Loop Sampling System Selection
What is a closed-loop grab sampling system?
A closed-loop grab sampling system collects a representative sample from a process media and routes all displaced material, purge fluid, and vapors back to the process line. Nothing vents to the atmosphere during collection, unless desired. This design eliminates operator exposure to hazardous materials and prevents fugitive emissions. Refining, petrochemical, and chemical processing operations use closed-loop systems for toxic, flammable, or high-vapor-pressure streams. Operators must not release these components during routine sampling.
What is the difference between gas/vapor sampling and liquefied gas sampling?
Gases and vapors sampling applies when the sample exists as a gas or vapor at collection conditions. Cylinder collection captures it in its vapor phase. Liquefied gas sampling applies when the stream stays liquid only because of elevated operating pressure. At ambient pressure, it flashes to vapor. Cylinder systems with sight glass outage verification confirm appropriate outage before disconnection. A bottle system for either stream type causes flash, sample loss, and safety hazards.
When do you need a heated sampling system?
You need a heated system when your stream solidifies or thickens beyond workable limits at collection temperature. Any stream with a pour point above ambient falls into the Heavy Liquids category. So does any stream with viscosity that blocks flow below 150 degrees F. SENSOR designs these systems with heated sample lines, heated collection containers, and high-temperature valve packing. Heavy liquid service runs from 300 to over 650 degrees F at the sample point.
What falls under Engineered Solutions?
Engineered Solutions covers applications where standard category systems cannot meet the process conditions, safety requirements, or installation constraints. HF acid service and streams above 800 degrees F or below -50 degrees F fall under this category. So do pressures above 3,000 psig, multi-phase streams, confined space installations, and multi-point collection panels. SENSOR engineers every Engineered Solution from your process data and site requirements. Custom drawings go through your review and approval before fabrication starts.
What Media do SENSOR Sampling Systems work with?
SENSOR designs systems for hydrofluoric acid, naphtha, heavy gas oil, residuum, hydrotreater streams, reactor effluent, and vacuum tower bottoms. SENSOR also covers refinery gas, hydrogen, propane, butane, pentane, and ethylene. Additional applications include ethylene dichloride, vinyl chloride monomer, and hydrogen chloride. Sulfuric acid, sodium hydroxide, phosgene, organic acids, and ethylene oxide are included. So are propylene oxide, olefins, styrene monomer, ethylbenzene, organic alkyls, and amines.
Does SENSOR Sampling Systems supply spare parts and consumables?
Yes. SENSOR Sampling Systems supplies all consumables and spare parts needed to keep closed-loop sampling systems running correctly. The inventory covers sample bottles, caps, septums, seals, cylinders, fittings, coolers, regulators, valves, hoses, and gauges. SENSOR parts fit sampling systems from any manufacturer, not only SENSOR-built equipment. Your facility sources all replacement parts from a single supplier, regardless of the original equipment supplier. Parts ship at off-the-shelf speed.
For a full spare parts strategy, read Designing a Spare Parts Strategy for Closed-Loop Sampling Systems.
How do I contact SENSOR Sampling Systems for an application consultation?
Contact SENSOR Sampling Systems at samplingorders@sorinc.com or submit a Request for Quote here. Bring your process data, including stream identity, vapor pressure, operating pressure, and temperature, and any site constraints. SENSOR engineers will identify the right category, confirm design requirements, and begin the engineered-to-order process.
Ready to Specify Your System?
Contact SENSOR Sampling Systems with your process data. Our applications engineers identify the right category, confirm your design requirements, and begin the engineered-to-order process.
Critical Maintenance for Closed Loop Grab Sampling Systems Whitepaper: Download the Whitepaper
Closed Loop Grab Sampling Handbook: Download the Handbook
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