OFITE Model 25 Constant-Speed Stirrer, 1 L

Overview

The OFITE Model 25 Constant-Speed Stirrer is a precision-engineered laboratory instrument designed to meet the rigorous mechanical mixing requirements specified in API RP 10B-2 (for oilwell cement slurries) and API RP 19C (for hydraulic fracturing fluids). It operates on a closed-loop microprocessor-controlled DC motor system that maintains set rotational speed with high reproducibility—regardless of load-induced torque variations, line voltage fluctuations, or changes in sample viscosity. Unlike variable-speed stirrers requiring manual intervention, the Model 25 delivers protocol-compliant, time-synchronized agitation sequences essential for standardized rheological conditioning prior to fluid loss, thickening time, or gel strength testing. Its dual-mode architecture—cement (CEM) and fracturing fluid (FRAC)—ensures strict adherence to API-defined shear histories, enabling laboratories to generate repeatable, auditable slurry preparation data under GLP or ISO/IEC 17025-compliant workflows.

Key Features

• Microprocessor-regulated speed control ensures ±1.5% speed stability across full load range—critical for API-mandated shear history replication
• Dual preprogrammed modes: CEM mode (4000 rpm × 15 s → 12,000 rpm × 35 s) and FRAC mode (1500 rpm × 300 s), both fully automated with sequential timing and speed transitions
• Three user-definable programs plus continuous variable-speed operation (0–25,000 rpm in CEM mode; 0–5,000 rpm in FRAC mode) for method development and non-API applications
• Stainless-steel impeller with optimized blade geometry for uniform axial flow and minimal vortex formation in 1 L vessels
• High-contrast digital LED display with real-time rpm readout, elapsed time countdown, and mode/status indicators
• Universal power input (115 V / 60 Hz or 230 V / 50 Hz) with internal voltage regulation to eliminate speed drift during brownout conditions
• Robust cast-aluminum housing with integrated thermal protection and overload cutoff

Sample Compatibility & Compliance

The Model 25 accommodates two distinct vessel configurations: a 1 L stainless-steel cup (supplied with #120-64-1 units) for cement slurry preparation per API RP 10B-2 Annex A, and a 1 L borosilicate glass cup (supplied with #120-64-1-F units) for fracturing fluid mixing per API RP 19C Section 5. Both cups are dimensionally calibrated to ensure consistent fluid depth-to-impeller immersion ratios—directly impacting shear rate distribution and API test validity. The instrument conforms to IEC 61010-1:2010 safety standards for electrical equipment used in laboratory environments and supports traceable calibration via external tachometer verification. Its operational parameters align with ASTM D6988 (Standard Practice for Preparing Cement Slurries) and ISO 10422 (Petroleum and natural gas industries — Drilling fluid systems — Performance evaluation).

Software & Data Management

While the Model 25 operates as a standalone hardware platform without embedded PC connectivity, its deterministic timing logic and repeatable speed profiles enable seamless integration into LIMS and electronic lab notebook (ELN) ecosystems via manual entry or barcode-scanned protocol logs. Each run generates an immutable sequence record—including mode selection, start time, total duration, and final rpm—supporting 21 CFR Part 11-compliant audit trails when documented within validated digital workflows. Optional third-party data loggers (e.g., USB-connected tachometers with timestamped CSV export) can capture real-time rpm vs. time curves for method validation reports required under GMP or API Q1 quality management systems.

Applications

• Preparation of API-standard oilwell cement slurries for thickening time (ASTM C109/C109M), fluid loss (API RP 10B-2), and compressive strength testing
• Hydraulic fracturing fluid formulation per API RP 19C, including guar-based, synthetic polymer, and crosslinked gels
• Rheological preconditioning of drilling muds prior to viscometer analysis (Fann 35A, DV2T)
• Accelerated aging studies involving high-shear mixing of cement additives (e.g., retarders, dispersants, nanosilica)
• QC/QA batch release testing in cement additive manufacturing facilities and service company labs

FAQ

Does the Model 25 comply with API RP 10B-2 Section 7.3.2 for cement slurry mixing?
Yes—the CEM mode executes the exact sequence: 4000 rpm for 15 seconds followed by 12,000 rpm for 35 seconds, using the specified stainless-steel cup and impeller geometry.
Can the same unit be used for both cement and fracturing fluid protocols?
Yes, but vessel type must match the selected mode: stainless-steel cup for cement, glass cup for fracturing fluids. Units are configured at time of order (#120-64-1 vs. #120-64-1-F).
Is speed calibration traceable to NIST standards?
The instrument does not include built-in calibration; however, speed accuracy is verifiable using a NIST-traceable optical tachometer, and OFITE provides calibration certificates upon request for third-party verification.
What maintenance is required to sustain long-term speed accuracy?
Annual inspection of carbon brushes and impeller shaft alignment is recommended; OFITE supplies replacement brush kits (P/N 120-64-BRUSH) and offers certified recalibration services.
Does the unit support remote start/stop or RS-232 output?
No—it is a manually operated, self-contained device with no communication ports. All control is local via front-panel membrane switches.