Formulation and mixing vessel
Compounding vessel · Mixing tank · Holding vessel · Bulk solution vessel
The jacketed, agitated vessel where a bulk solution is compounded and held before filtration, and the cleaning, sterilisation and hold times that keep it fit for use.
What this page does not claim
An equipment family page teaches how a kind of equipment works and how it is assured. It is not a qualification of any site’s equipment, sets no universal limits, and was checked by SPEQ against the sources it lists, not by an independent engineer.
WHAT IT DOES
Ingredients are added to water for injections in a stainless steel (or single-use) vessel, mixed to a uniform solution at a controlled temperature, sampled, and transferred by pressure or pump through the sterilising filter. Chapter 3 asks that product-contact parts "must not be reactive, additive or absorptive" to an extent that affects quality (3.39).
For sterile products, the bulk is usually filtered to reduce bioburden before filling, with "a maximum permissible time between preparation and filling" (Annex 1, 8.5). A vessel sterilised in place stays integral, under positive pressure or behind a sterilising vent filter, until use (Annex 1, 8.63).
Where it sits: In the preparation area (grade C or D for most sterile products), between dispensing and sterile filtration.
WHERE YOU FIND IT
- Compounding of parenteral solutions
- Holding of sterile-filtered bulk before filling
- Buffer and media preparation
In the reference facility: Processing & formulation suite
Not covered on this page: Bioreactors and fermenters; Solid-dose blenders.
MAJOR COMPONENTS
- Vessel with jacket. Holds product; the jacket heats or cools it.
- Agitator (top or bottom mounted, magnetically coupled). Mixes the solution; seal design affects cleanability and contamination risk.
- Load cells. Weigh additions and batch volume.
- Spray device, vent filter and rupture disc. Cleaning coverage, sterile venting (Annex 1, 8.88) and over-pressure protection.
- Sampling valve. Takes in-process samples without contaminating the batch.
- Labelled fixed pipework. Shows contents and flow direction (Chapter 3, 3.42).
Connects to: WFI system; Dispensing (weighed ingredients); CIP and SIP systems; Sterilising filter assembly; Process gases for pressure transfer.
INSTRUMENTS AND WHAT THEY MEASURE
- Balance or load cell. Batch weight from load cells under the vessel. Watch for: weighing below the balance's minimum weight for the required accuracy.
- Temperature sensor (RTD or thermocouple). Product temperature during compounding and hold. Watch for: sensor not at the location that matters (cold spot, load centre).
- Pressure transmitter (gauge or absolute). Vessel pressure during transfer, SIP and hold. Watch for: gauge and absolute values compared directly.
- Filter integrity tester. Integrity of the vent filter after use (Annex 1, 8.88). Watch for: membrane not fully wetted, giving a false failure.
PARAMETERS
SETPOINT · MEASURED · LIMIT · ATTRIBUTE- Weighed mass (measured, g or kg). Batch and addition weights, on load cells of suitable range and precision (Chapter 3, 3.40).
- Agitation speed (setpoint, rpm). For the product and fill volume, as established in process validation.
- Temperature (setpoint, °C). Compounding and hold temperature for the product.
- Dirty and clean hold time (limit, h or days). Maximum time from preparation to filtration and filling, defined by the site for each product (Annex 1, 8.5, 8.18).
- Pre-filtration bioburden (limit, CFU/100 mL or CFU/mL). Sampled from the bulk before filtration, against the site’s limit (Annex 1, 8.93).
SPEQ publishes no universal alarm or acceptance values: they depend on the process, the product and the site’s own qualification.
CONTROLS, ALARMS AND INTERLOCKS
- Control loop: Temperature and agitation control. Holds the compounding conditions.
- Safety function: Over-pressure protection. Rupture disc or relief valve protects the vessel and people; its basis is pressure safety.
- Interlock: Agitator low-level interlock. Stops the agitator when the level is below the impeller.
- Procedure: Calibration of measuring equipment. Load cells and instruments calibrated and checked at defined intervals (Chapter 3, 3.41).
An alarm asks for a response; an interlock stops an action; a safety function protects people and has its own risk basis.
HOW IT FAILS
- Incomplete mixing at a different fill volume. Non-uniform bulk.
- Agitator seal wear. Particles or lubricant in product, and a site that resists cleaning.
- Hold time exceeded. Bioburden growth before filtration (Annex 1, 8.5).
- Hoses bearing on the vessel. Load cell readings wrong.
- Loss of positive pressure after SIP. Sterilised vessel recontaminated (Annex 1, 8.63).
ASSURANCE ACROSS THE LIFECYCLE
EXAMPLES, NOT A MANDATORY LIST- Design and qualification. Product-contact materials (Chapter 3, 3.39); Cleanable design and drainability (3.36); Load cell accuracy across the range.
- Process validation. Mixing uniformity at minimum and maximum volumes; Hold time studies with bioburden.
- Cleaning and SIP. Cleaning validation (Annex 15, § 10); SIP validation with slowest-to-heat locations (Annex 1, 8.63).
- Routine. Batch records of weights, times and temperatures; Calibration records (Chapter 3, 3.41).
WHAT THIS DOES NOT PROVE
- Mixing for the set time and speed does not prove the solution is uniform. Instead: Uniformity results from mixing validation at worst-case volumes.
- A clean, sterilised vessel does not prove the bulk stayed within its bioburden limit during hold. Instead: Pre-filtration bioburden results and hold time records.
SOURCES
3 CITED- EU GMP Part I, Chapter 3: Premises and Equipment — European Commission (EudraLex Volume 4), 13 August 2014, in operation 1 March 2015. European Union; in force. Supports: Design for intended purpose (3.34); cleanable design (3.36); installation (3.38); product-contact materials (3.39); balances and measuring equipment (3.40, 3.41); labelled pipework (3.42).
- EU GMP Annex 1: Manufacture of Sterile Medicinal Products — European Commission (EudraLex Volume 4), 2022 revision, in operation 25 August 2023. EU / EEA; revised jointly with the PIC/S Committee; in force. Supports: Bioburden-reduction filtration and maximum time to filling (8.5); validated times (8.18); steam-in-place and integrity after SIP (8.63); vent filters (8.88); bioburden sampling (8.93).
- EU GMP Annex 15: Qualification and Validation — European Commission (EudraLex Volume 4), 2015. EU / EEA; in force. Supports: Cleaning validation (§ 10) and process validation approach.
HOW THIS PAGE WAS CHECKED
Researched and checked against the sources above by SPEQ (Claude) on 2026-10-21. It has not been reviewed by an independent engineer. It teaches how this kind of equipment works and is assured; it does not say any site, asset or process is qualified, validated or compliant.
- Single-use mixing systems share most of this page; extractables and leachables are not yet covered here.
Spotted something wrong? Tell us.