How to Specify Closed Loop Extraction Systems: Pressure Ratings, Recovery Architecture, and the Documentation Package
A closed loop extraction system is a sealed processing platform in which solvent moves from a storage vessel, through a material column packed with botanical material, into a collection base, and then back to storage through a recovery leg — without venting into the room. The "loop" is that recovery leg. Every other component on the skid exists to serve it.
This guide is written for the buyer specifying equipment, not the reader learning the term. If you are locking system specs before a facility buildout or replacing an aging platform before the next processing cycle, four decisions determine what your operation can actually run: how you size the system, which recovery architecture you buy, how the equipment integrates with a classified room, and what documentation arrives on the truck with it.
What does "closed loop" actually specify — and what does it not?
Closed loop specifies containment: solvent stays inside the process boundary from storage vessel, through the material column and collection base, and back to storage. It does not specify which solvent you run — the architecture applies to ethanol and hydrocarbon platforms alike.
What does the architecture contain?
Closed loop describes containment. Solvent is charged from a storage vessel, contacts feedstock in the material column, carries botanical oil into the collection base, and is then driven off and condensed back to storage. Sight glasses, pressure relief valves, tri-clamp fittings and jacketed vessels are the hardware that makes that circuit observable, serviceable and repeatable.
The comparison worth one sentence: uncontained open-solvent processing is a hobbyist practice, not a procurement option, and no licensed processor is choosing between it and a commercially manufactured platform. The real question is how well a given system is engineered to keep solvent out of the room and inside the loop, which is what how closed-loop extraction systems contain solvent during processing covers in detail.
Is "closed loop" a hydrocarbon-only term?
No. Closed loop applies equally to ethanol and hydrocarbon platforms. The architecture is solvent-agnostic: any system that circulates solvent through material and recovers it back to storage within a sealed boundary is closed loop, whether that solvent is butane, propane or ethanol.
Most vendor and forum literature silently equates closed loop with butane and propane, while the patent literature defines it solvent-agnostically. Our automated ethanol extraction systems — the EES Series, the semi-automated M Series, CES Series centrifuge extraction and ASR Series solvent recovery — are closed loop by the same structural test that applies to our hydrocarbon extraction equipment, the automated AHES Series and the operator-driven MHES Series. If a vendor tells you closed loop means hydrocarbon only, they are describing their catalogue rather than the technology.
How do you size a closed loop system against daily throughput?
Size on cycle time, not on column capacity. Fix your target output per shift, work backward through full cycle time, size the recovery architecture to hit that cycle time, and size the material column last.
The most expensive specification error we see is sizing on material column capacity alone. Column capacity is a batch figure. Daily output is a function of cycle time, and cycle time is dominated by solvent recovery and turnaround rather than by the extraction step itself.
Why does stated column capacity differ from realized daily output?
Stated column capacity assumes a packing density. Vendors calculate to an upper limit, and low-density or lightly packed feedstock will not reach it. Put the question to every vendor directly: what packing density is your stated column capacity calculated at? A system quoted at a density your material cannot achieve will underperform its spec sheet on day one, and no amount of process tuning recovers that gap.
How do you work backward from output per shift?
Use a procedure instead of a number:
- Fix your target output per shift, with the run cadence you actually intend to operate.
- Work backward through full cycle time — charge, extraction, recovery, discharge, column repack and cleanout.
- Size the recovery architecture to hit that cycle time.
- Size the column last.
That ordering produces predictable cycle times and output you can plan a production schedule around. The reverse ordering produces a large column and a recovery leg that cannot keep up with it. We build the EES Series ethanol extraction systems and the AHES Series automated hydrocarbon extraction systems across capacity tiers specifically so this conversation happens before quoting rather than after installation. For the underlying math, see measuring and scaling extraction system throughput.
Is passive or active solvent recovery better?
Neither is better in the abstract; the choice follows batch cadence. Passive recovery fits low daily volumes and a single-batch cadence. Active recovery fits back-to-back batches on a fixed schedule, where recovery speed is the constraint on the whole facility.
Passive recovery moves solvent using temperature and pressure differential alone — heat the collection side, chill the receiving vessel, and vapor migrates and recondenses through the condensing coil. Nothing mechanical sits in the vapor path. Active recovery adds a recovery pump that compresses vapor from the collection side into the recovery vessel, with condensing on the pump outlet. The two architectures are therefore limited by different things and are serviced in different places.
| Passive recovery | Active recovery | |
|---|---|---|
| Vapor path | Thermal and pressure differential only | Pump-driven compression |
| What drives the recovery rate | The differential between the heated collection side and the chilled receiving vessel | The recovery pump, with condensing on the pump outlet |
| Cycle time | Longer, less controllable | Shorter, schedule-controllable |
| Utility load / chilling dependence | High — relies on recirculating chiller capacity and differential | Lower chilling dependence; adds the recovery pump to the utility list |
| Maintenance and service point | Minimal moving parts in vapor path; performance tracks chiller capacity and differential | Pump service and periodic rebuild |
| Documentation implication | Recovery rate demonstrated at factory acceptance testing, in writing | The same factory acceptance test evidence, plus confirmation that vessels, lines and valves are rated for the higher flow |
| Best fit | Low daily volumes, single-batch cadence | Back-to-back batches on a fixed schedule |
Where does the crossover sit?
It depends on your batch cadence, not on a pounds-per-day threshold. If you run one batch and then break down the column, passive is workable. Once you are running batches back-to-back against a production schedule, recovery speed becomes the constraint on the entire facility, and active recovery is the practical answer.
Treat recovery performance as something to verify rather than accept. Require the vendor to demonstrate recovery rate during factory acceptance testing, with your material or a representative surrogate, and get the result in writing as documented recovery performance. A recovery figure quoted without a stated measurement method and material is not comparable between vendors.
Can a passive system be upgraded to active recovery later?
Ask before you buy. One procurement question almost nobody asks: can this passive system be retrofitted with active recovery later, and are the vessels, lines and valves rated for the higher flow? Buying a platform that cannot be upgraded is a common and expensive mistake, because the growth curve usually arrives before the depreciation schedule does. On the ethanol side, our ASR Series automated solvent recovery is the architecture answer, and both the EES and AHES platforms are engineered around recovery capability first.
What does an ASME rating cover, and which vessels need it?
ASME BPVC Section VIII, Division 1 applies to pressure vessels operating at internal or external pressures above 15 psig, and the certification mark is carried by individual vessels rather than by a system as a whole. The buyer's question is which vessels carry it, with documentation for each.
What does an ASME rating actually cover?
ASME BPVC Section VIII, Division 1 sets requirements for the design, fabrication, inspection, testing and certification of pressure vessels operating at internal or external pressures exceeding 15 psig, and contains the rules governing use of the U, UM and UV ASME Product Certification Marks. That is the whole substance of the mark: a design basis, an inspection record and a certification trail.
Which means the buyer's question is not "is the system ASME?" It is: which vessels carry the mark, and can I see the documentation for each one? Ask specifically about the solvent storage vessel, the collection base and the material columns, component by component. A general claim that a system is ASME, offered without paperwork, is a marketing badge rather than a documentation trail. MACH equipment is built to CE, IECEx, UL 508A, PSI and ASME compliance marks.
Which product-contact materials should you specify?
Product-contact surfaces should be sanitary-grade stainless — 304 and 316L — with tri-clamp interfaces and gasket materials selected for your solvent and wash-down chemistry. Cleanability is a throughput variable. Changeover time between runs and the risk of cross-batch carryover both track directly to how the wetted path is built. Where color remediation columns (CRC), molecular sieve driers or in-line filtration are part of the configuration, they add wetted surfaces and cleaning steps that belong in your cycle-time model.
This is also why we design, fabricate, assemble and test every system in our vertically integrated Michigan facility, selling nationally across the United States. Fabrication control is what makes a complete documentation package possible in the first place.
How do you specify the extraction system and the classified room together?
Specify them during design, not at inspection. The classification is set by your Authority Having Jurisdiction and fire code official, classified areas must be documented under OSHA 29 CFR 1910.307, and unrated ancillaries have to be located outside the classified space.
What documentation does a classified location require?
OSHA 29 CFR 1910.307 establishes the Class I, Division 1 and Division 2 hazardous (classified) location designations and requires that areas designated as classified be properly documented, with that documentation available to everyone authorized to design, install, inspect, maintain or operate electrical equipment at the location. Most buyers discover this obligation during inspection. Handle it during design.
The distinction itself is straightforward. A Class I, Division 1 area is one where ignitible concentrations of flammable vapor can be present under normal operating conditions. A Division 2 area is one where those concentrations are expected only under abnormal conditions, such as a container failure or a ventilation system fault. That difference drives the rating requirement on every electrical component in the room, and the classification decision is made with your Authority Having Jurisdiction and fire code official, informed by NFPA 70 (National Electrical Code) Article 500.
The same OSHA standard lists ten acceptable protection techniques for classified locations — purged-and-pressurized systems, intrinsically safe circuits, hermetically sealed devices and others — rather than a single mandatory approach. So the correct question about any component is "is it rated for the area classification?" and there is more than one compliant path to yes. Our primer on C1D1 and C1D2 environments in botanical extraction facilities walks through what changes between them, and preparing for NFPA 420 covers the facility-side review.
Where do the unrated ancillaries go?
Outside the classified area. Here is the integration detail that forces rooms to be redesigned twice: recirculating chillers, heaters, vacuum pumps and air compressors supporting the system are frequently not rated for the classified space and must be located outside it. Utility routing, penetrations and equipment placement have to be resolved during layout, well before commissioning, when the concrete is poured and the panel schedule is fixed.
Detection, ventilation and interlocks belong in the same conversation. They are system elements rather than accessories bolted on at the end, and their setpoints and rates are set by your jurisdiction rather than by an equipment brochure. Our engineering team supports both Division 1 and Division 2 strategies, and the EE-1 and EE-2 Series enclosures are designed to support a classified environment around the extraction system, subject to AHJ review — see the EE-2 Series extraction enclosures and our turnkey extraction systems and lab buildouts.
What documentation should arrive with a closed loop extraction system?
Eight items: the serial number, pressure vessel documentation, per-component certification marks, the control panel listing, the drawings, the manual and SOPs, the factory acceptance test records, and the spare parts list. Assemble the list below before you order.
- Serial number permanently affixed and visible on the unit
- Pressure vessel documentation for each vessel, identified individually
- Certification marks identified per component, with supporting paperwork
- Control panel listing — UL 508A for the industrial control panel
- P&IDs and general arrangement drawings
- Operating manual and draft SOPs
- Factory acceptance test records, including recovery performance
- Recommended spare parts list with lead times
A manufacturer that designs, fabricates, assembles and tests in one facility can produce this package as a matter of course. An importer or reseller assembling third-party components generally cannot, because it does not hold the fabrication records the certification trail depends on.
What does one state's rule require, and what is the pattern behind it?
As a representative example, Washington State Legislature, WAC 314-55-104 requires closed loop systems to be commercially manufactured and to bear a permanently affixed, visible serial number, and requires certification from a licensed engineer — carrying the professional engineer's signature, stamp and the unit's serial number — that the system was commercially manufactured, safe for its intended use, and built to recognized and generally accepted good engineering practices such as ASME, ANSI, UL or ASTM.
That is one state's approach, not a national requirement. Requirements vary by state and by AHJ. But the recurring pattern is consistent across jurisdictions: commercially manufactured equipment, a traceable serial number, a professional engineer's certification, and construction to recognized standards. A buyer who confirms all four before purchase is positioned for review in most jurisdictions. Confirm the specifics with your own AHJ, fire code official and licensing authority.
What should installation, commissioning and training include?
A complete commissioning scope spans factory acceptance testing before shipment, site acceptance testing after set and utility connection, leak and pressure checks, supervised first runs with your own feedstock, and a signed handover record tied to the unit serial number.
Installation and commissioning are specification line items. So is training. Unplanned downtime and operators who need too much supervision to run a system safely are usually described as operational problems, but they were procurement decisions made at purchase.
Scope commissioning in writing before you sign. A complete scope usually spans factory acceptance testing before shipment, site acceptance testing after set and utility connection, leak and pressure checks on the assembled circuit, supervised first runs with your own feedstock, and a signed handover record that ties back to the unit serial number. Each of those steps produces a document your reviewer or insurer may later ask for.
Automation narrows operator-to-operator variance and shortens the ramp for new staff, which is the strongest honest argument for an automated platform such as EES, AHES or ATS Pro at a facility that is hiring and scaling. The counter-case is real too: operator-driven systems like the M Series and MHES Series suit facilities with experienced staff and a lower cadence, and they carry a lower acquisition cost. Choose on staffing reality rather than on the spec sheet.
Data logging matters to a capital buyer for two reasons: batch reproducibility, and having a process record when a reviewer, an insurer or a customer asks how a lot was produced. MACH provides installation, operator training, and technical support on demand for the systems we build.
How do you match a system to your operation?
Ethanol platforms favor high-volume throughput and broad-spectrum crude destined for downstream refinement; hydrocarbon platforms favor terpene-forward and specialty product targets. Neither is categorically better — the choice follows your product target, facility classification burden and staffing.
Ethanol platforms favor high-volume throughput and broad-spectrum crude destined for downstream refinement — winterization, decarboxylation, distillation and isolate work. Hydrocarbon platforms favor terpene-forward and specialty product targets. Facility classification burden, solvent handling and storage, and your post-processing train all shift with that choice. Neither is categorically better; we manufacture both, and the honest framing is how to choose. Choosing between ethanol and hydrocarbon systems works through the tradeoffs in more depth.
Which eight questions should you put to a vendor before signing?
- What packing density is your stated column capacity based on?
- Which vessels carry which certification marks, and can I see the documentation?
- Is the control panel listed?
- Can this system be upgraded from passive to active recovery later?
- Which ancillaries sit outside the classified area?
- What arrives in the documentation package?
- What does installation and operator training include?
- What is the spare parts lead time?
If you are sizing a platform or laying out a classified room, talk to our engineering team about system specification before the drawings are frozen. That conversation is where a six-figure capital purchase either fits the facility or fights it.
Frequently asked questions
What is a closed loop extraction system, and what does the "loop" actually refer to?
It is a sealed system in which solvent moves from a storage vessel, through a material column packed with botanical material, into a collection base, and is then recovered and condensed back to storage. The "loop" is the recovery leg that returns solvent to the storage vessel.
Does "closed loop" only mean hydrocarbon, or does it apply to ethanol systems too?
It applies to both. Closed loop describes a containment architecture, not a solvent. Automated ethanol systems such as the EES Series and M Series meet the same structural definition as hydrocarbon systems such as the AHES and MHES Series.
What is the practical difference between passive and active recovery?
Passive recovery moves solvent with temperature and pressure differential alone and depends on recirculating chiller capacity; active recovery moves it with a recovery pump, with condensing on the pump outlet. Passive has minimal moving parts in the vapor path; active requires pump service and periodic rebuild and delivers shorter, schedule-controllable cycle times.
Can a passive system be upgraded to active recovery later?
Sometimes, and you should confirm it before purchase. Ask whether the vessels, lines and valves are rated for the higher flow an active recovery pump introduces. If they are not, the upgrade means new hardware rather than an added pump.
How do you verify a vendor's stated recovery rate?
Require a demonstration during factory acceptance testing, using your material or a representative surrogate, and take the result in writing as documented recovery performance. Recovery figures vary with input material, system configuration and process parameters, so a number quoted without its measurement conditions is not comparable between vendors.
What does an ASME rating on a pressure vessel actually cover?
ASME BPVC Section VIII, Division 1 covers design, fabrication, inspection, testing and certification for vessels operating above 15 psig, and governs use of the U, UM and UV Product Certification Marks. It applies to individual vessels — ask which ones in your system carry it.
Why does a system need a permanently affixed serial number?
Traceability. A serial number ties a specific unit to its engineer certification, its pressure vessel documentation and its factory test records. Washington's processor extraction rule requires exactly that linkage, and reviewers in other jurisdictions commonly look for it.
What is the difference between Class I Division 1 and Class I Division 2, and who determines the classification?
Division 1 covers areas where ignitible vapor concentrations can be present during normal operation; Division 2 covers areas where they are expected only under abnormal conditions such as equipment failure. Your Authority Having Jurisdiction and fire code official determine the classification, informed by NFPA 70 Article 500.
Which ancillary equipment has to be located outside the classified area?
Typically recirculating chillers, heaters, vacuum pumps and air compressors, unless each unit is specifically listed for the area classification. Resolve placement and utility routing during layout, and confirm the classification boundary with your AHJ.
How much operator training does an automated system require compared with an operator-driven one?
Automated platforms shorten the ramp and reduce variance between operators, because process sequencing is controlled by the system rather than by technique. Operator-driven platforms assume experienced staff and a lower run cadence.
What is included in installation, commissioning, and ongoing technical support?
MACH provides installation, operator training and on-demand technical support for the systems it manufactures. Commissioning typically spans factory acceptance testing, site acceptance testing, leak and pressure verification, supervised first runs and a signed handover record. Confirm the scope of each in writing at quote stage, alongside the spare parts list and lead times.
Important disclosures
Extraction equipment must be installed, permitted, and operated in accordance with all applicable federal, state, and local fire, building, and electrical codes, including Class I Division 1 requirements where applicable. Consult your Authority Having Jurisdiction (AHJ) before installation.
Throughput, yield, purity, and solvent recovery figures vary with input material, system configuration, and process parameters. Published figures are not a guarantee of results.
MACH Technologies manufactures and sells processing equipment. It does not cultivate, produce, sell, or distribute any botanical end product.
Nothing on this site is medical advice, and no MACH Technologies equipment or the products made with it are represented as diagnosing, treating, curing, or preventing any disease.
Operators are responsible for verifying that their intended use is lawful in their jurisdiction.