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KRÜSS PT31 Peltier Circulation Thermostat
The KRÜSS PT31 Peltier Circulation Thermostat is an exceptionally compact laboratory temperature-control system designed for external temperature conditioning of refractometers, polarimeters, and other temperature-sensitive analytical instruments. Using thermoelectric Peltier technology rather than a conventional compressor refrigeration system, the PT31 provides both heating and cooling across an 8°C to 35°C temperature range with ±0.2°C temperature-control accuracy.
Available used and refurbished from American Instrument Exchange, the KRÜSS PT31 weighs only 1.5 kg and requires approximately 100 mL of heat-transfer fluid. Its compact footprint, low fluid volume, 20 L/h circulation pump, and simple digital controls make it particularly useful when precise instrument temperature control is required but a conventional refrigerated circulator would be unnecessarily large. A 90-day warranty is included.
Key Features
Peltier thermoelectric heating and cooling
8°C to 35°C temperature-control range
±0.2°C temperature-control accuracy
0.1°C temperature resolution
30 W heating capacity
20 W cooling capacity at 20°C
20 L/h pump capacity
20 mbar pump pressure
Approximately 100 mL filling volume
Compact 108 × 199 × 145 mm footprint
Bright two-line LCD matrix display
Suitable for water or water/glycol mixtures
Universal 100–240 V, 50/60 Hz operating voltage
Used, refurbished, and tested by American Instrument Exchange
90-day warranty included
Overview
The KRÜSS PT31 is fundamentally different from a conventional refrigerated laboratory chiller. Instead of using a compressor and refrigerant circuit, the PT31 employs Peltier thermoelectric technology to heat or cool a small volume of circulating fluid.
This approach allows KRÜSS to package both heating and cooling into an unusually compact instrument. The PT31 measures approximately 108 mm wide, 199 mm high, and 145 mm deep and weighs only 1.5 kg without its power adapter and cable.
The small 100 mL fluid volume also allows the PT31 to operate without the larger reservoir associated with traditional refrigerated circulators. It is intended for applications where a relatively small amount of temperature-controlled fluid needs to be continuously circulated through an external analytical instrument.
KRÜSS specifically designed this type of circulation thermostat for temperature-sensitive measurement equipment, making the PT31 particularly appropriate for refractometers, polarimeters, and similar analytical systems where sample or measuring-cell temperature can directly affect results.
Key Specifications
Specification
Details
Manufacturer
A. KRÜSS Optronic
Model
PT31
Equipment Type
Peltier circulation thermostat
Temperature-Control Range
8°C to 35°C
Temperature-Control Accuracy
±0.2°C
Temperature Resolution
0.1°C
Ambient Temperature Range
5°C to 40°C
Heating Capacity
30 W
Cooling Capacity at 20°C
20 W
Pump Capacity
20 L/h
Pump Pressure
20 mbar / approx. 0.29 psi
Filling Volume
Approx. 100 mL
Display
Two-line LCD matrix display
Compatible Fluids
Non-flammable liquids such as water or water/glycol mixtures
IP Rating
IP21
Dimensions
108 mm W × 199 mm H × 145 mm D
Weight
1.5 kg, excluding power adapter and cable
Operating Voltage
100–240 V AC, 50/60 Hz
Maximum Power Consumption
80 W
Warranty
90 days
Common Applications
The KRÜSS PT31 is designed primarily for external temperature control of analytical instruments and small-volume laboratory systems. Refractometry and polarimetry are especially relevant applications because measured optical properties can vary with sample temperature.
Circulating temperature-controlled fluid through a compatible refractometer can help maintain the measuring prism and sample at a consistent temperature during analysis. Similar temperature control can be valuable for polarimeters and other analytical systems where measurement accuracy or reproducibility depends on stable sample conditions.
The PT31 may also be suitable for other small-volume external temperature-control applications when the required temperature, flow, pressure, and thermal load fall within the unit's capabilities.
Ideal Laboratory Types
The KRÜSS PT31 is particularly well suited for analytical chemistry, pharmaceutical quality control, food and beverage testing, chemical manufacturing, academic research, cosmetics testing, and other laboratories using temperature-sensitive optical measurements.
Its exceptionally small footprint can be advantageous in laboratories where multiple analytical instruments share limited bench space. Instead of dedicating floor or under-bench space to a conventional recirculating chiller, the PT31 can be positioned close to the instrument it serves.
Its low fluid volume and straightforward operation can also make it practical as a dedicated thermostat for a single analytical workstation.
Temperature Control & Stability
The KRÜSS PT31 provides temperature control from 8°C to 35°C with ±0.2°C temperature-control accuracy and 0.1°C display resolution.
Peltier technology allows the unit to both heat and cool without the compressor used in a conventional refrigerated circulator. Electrical current through the thermoelectric system transfers heat in the required direction, allowing the PT31 to maintain the circulating fluid at the selected temperature.
The PT31 provides 30 W of heating capacity and approximately 20 W of cooling capacity at a fluid temperature of 20°C.
This relatively modest thermal capacity is appropriate for the PT31's intended role as a small analytical-instrument thermostat. It should not be confused with a laboratory chiller designed to remove hundreds or thousands of watts from heat-generating equipment.
The limits of the 8°C to 35°C temperature-control range also depend on suitable ambient conditions. KRÜSS specifies an ambient operating range of approximately 5°C to 40°C.
Circulation & Pump Performance
The PT31 provides a pump capacity of approximately 20 L/h with maximum pump pressure of approximately 20 mbar.
These figures are substantially lower than those of larger laboratory recirculating chillers, but that is intentional. The PT31 is designed to circulate a small volume of temperature-controlled fluid through compatible analytical instruments rather than drive coolant through long or highly restrictive process loops.
The system requires only approximately 100 mL of heat-transfer fluid. KRÜSS specifies operation with non-flammable liquids such as water or an appropriate water/glycol mixture.
Actual circulation will depend on tubing, fittings, fluid properties, elevation, and the resistance of the connected instrument. Laboratories should confirm compatibility before using the PT31 with equipment other than its typical analytical-instrument applications.
Refurbishment & Testing
This used KRÜSS PT31 Peltier Circulation Thermostat is refurbished and tested by American Instrument Exchange before shipment. Our technicians inspect the Peltier temperature-control system, circulation pump, display, controls, electrical components, fluid connections, and general operating condition.
Temperature-controlled equipment is tested using NIST-traceable probes and data loggers. Because the PT31 provides both heating and cooling, the system is operated to evaluate temperature regulation and circulation across representative portions of its operating range.
The fluid circuit and accessible fluid-contact components are also cleaned and inspected prior to shipment.
If your application requires operation at a particular temperature or has specific testing requirements, contact American Instrument Exchange before shipment. When practical, our technicians can incorporate customer-requested conditions into final testing.
A 90-day warranty is included with this refurbished KRÜSS circulation thermostat.
Choosing the Right Peltier Circulation Thermostat
The KRÜSS PT31 is best viewed as a compact analytical-instrument thermostat rather than a general-purpose laboratory chiller. Its greatest advantages are its small size, low fluid requirement, straightforward operation, and ability to both heat and cool without a conventional refrigeration system.
For temperature control of a compatible refractometer, polarimeter, or other small analytical instrument within the 8°C to 35°C range, the PT31 can provide a considerably smaller solution than a traditional refrigerated circulator.
Applications requiring subzero temperatures, high coolant flow, substantial pump pressure, or significant heat-removal capacity should instead use an appropriately sized refrigerated circulator or recirculating chiller.
American Instrument Exchange can help compare available used and refurbished laboratory circulators based on your instrument, required temperature range, thermal load, flow requirements, and available laboratory space.
Related Equipment
American Instrument Exchange stocks a variety of laboratory circulators, including compact circulation thermostats, refrigerated circulators, heated circulators, and recirculating chillers. Laboratories performing temperature-sensitive analytical procedures may also require laboratory water baths and other refurbished laboratory equipment for sample preparation and temperature control.
KRÜSS PT31 Frequently Asked Questions
What is the KRÜSS PT31 used for?
The KRÜSS PT31 is designed for external temperature control of compatible analytical instruments. Refractometers and polarimeters are particularly common applications because stable sample temperature can be important for accurate and reproducible optical measurements.
What is the temperature range of the KRÜSS PT31?
The PT31 provides temperature control from 8°C to 35°C under appropriate ambient operating conditions.
How accurate is the KRÜSS PT31?
KRÜSS specifies temperature-control accuracy of ±0.2°C with temperature resolution of 0.1°C.
Does the PT31 use a refrigeration compressor?
No. The PT31 uses Peltier thermoelectric technology for heating and cooling. This allows the system to provide temperature control in a much smaller package than a conventional compressor-based refrigerated circulator.
What is the pump capacity of the KRÜSS PT31?
The PT31 has a specified pump capacity of approximately 20 L/h with pump pressure of approximately 20 mbar. It is intended for small external temperature-control circuits rather than high-flow or high-pressure laboratory cooling applications.
How much fluid does the KRÜSS PT31 require?
The PT31 has a filling volume of approximately 100 mL. KRÜSS specifies compatible non-flammable heat-transfer liquids such as water or water/glycol mixtures.
Is the KRÜSS PT31 suitable for cooling high-heat-load equipment?
Generally, no. The PT31 provides approximately 20 W of cooling capacity at 20°C and is intended primarily for temperature conditioning of analytical instruments. Equipment generating substantial heat typically requires a larger recirculating chiller.
Does this refurbished KRÜSS PT31 include a warranty?
Yes. This used KRÜSS PT31 is refurbished and tested by American Instrument Exchange and includes a 90-day warranty.
Testing Procedures for Used and Refurbished Laboratory Equipment
Ensure Accuracy, Safety, and Dependable Performance Across Applications
At American Instrument Exchange, all used and refurbished laboratory equipment undergoes a rigorous, multi-point testing protocol to ensure optimal performance, operational safety, and long-term reliability. Whether the equipment is destined for research, diagnostics, quality control, or production environments, our thorough inspection and testing process is designed to meet the highest standards of laboratory excellence.
Why Testing Used Lab Equipment Is Essential
Before any refurbished laboratory equipment is returned to service, it must be carefully tested to verify:
• Functional integrity and operational performance
• Setpoint accuracy and repeatability (where applicable)
• User interface responsiveness and control features
Proper testing reduces the risk of equipment failure, measurement inaccuracies, or user hazards—helping to ensure consistent results in clinical, academic, biotech, and industrial labs.
Our standardized lab equipment testing procedures are tailored to each equipment type, ensuring every unit meets manufacturer specifications and industry benchmarks.
Key Testing Procedures for Refurbished and Used Laboratory Equipment
1. Initial Visual Inspection
• Examine equipment housing for signs of wear, corrosion, or damage
• Check ports, power cords, and exterior components for tampering or deterioration
• Verify that internal and external parts (racks, shelves, connectors, accessories) are present and undamaged
2. Functional Startup and Operational Testing
• Power on the equipment and verify startup diagnostics
• Confirm functionality of displays, buttons, switches, and control panels
• Run basic functions to confirm proper response and behavior under standard operating conditions
3. Testing and Performance Verification
• Test internal sensors or control systems using industry-standard tools
• Perform operational tests to validate accuracy and consistency
• Verify key performance specifications such as temperature control, timing, speed, or measurement outputs, depending on equipment type
4. Mechanical and Electrical System Testing
• Evaluate motors, pumps, fans, or other moving parts for smooth operation
• Inspect and test wiring, relays, fuses, and circuit boards for safety and reliability
• Test power delivery and grounding compliance
5. Safety and Compliance Checks
• Ensure equipment is grounded and insulated to meet laboratory safety standards
• Test alarms, interlocks, emergency stops, or safety shutdown systems if applicable
6. Final Quality Assurance and Documentation
• Perform extended runtime testing
• Document operational logs, testing results, and any repairs or adjustments made
• Complete a final inspection, thorough cleaning, and packaging for delivery
Trusted Quality from American Instrument Exchange
With over 50 years of experience in laboratory equipment refurbishment, American Instrument Exchange is committed to delivering certified, lab-ready instruments backed by expert testing. Our testing protocols ensure that each piece of equipment—regardless of type—is safe, accurate, and dependable from day one.
Whether you're equipping a startup lab or expanding a high-throughput facility, you can count on our refurbished laboratory equipment to perform with precision and reliability.
Refurbishment Protocol for Used Laboratory Equipment from American Instrument Exchange
At American Instrument Exchange, every piece of used laboratory equipment we offer undergoes a multi-step refurbishment process. Whether it's an analytical balance, centrifuge, freezer, oven, or any other essential lab instrument, our goal is to restore each unit to peak performance—ensuring accuracy, safety, and long-term reliability in scientific, clinical, industrial, and academic environments.
Why Choose Refurbished Lab Equipment from American Instrument Exchange?
• Thoroughly tested for performance, precision, and safety
• Backed by a warranty
• A cost-effective alternative to new equipment
• Environmentally sustainable through equipment reuse and waste reduction
• Serviced by expert technicians with decades of laboratory equipment experience
Step-by-Step Refurbishment Protocol
Every instrument and system refurbished at American Instrument Exchange follows a detailed, industry-aligned process:
1. Initial Intake & Inspection
• Complete visual and structural inspection for cosmetic damage, wear, or corrosion
• Mechanical assessment of hinges, seals, fasteners, motors, and moving parts
• Missing components and damaged items are documented for repair or replacement
2. Cleaning and Decontamination
• Full internal and external cleaning using non-abrasive, lab-safe solutions
• Removal of biological, chemical, or particulate contamination
• Disassembly and cleaning of removable parts such as trays, shelves, and filters
3. Mechanical and Electrical Repair
• Replacement or repair of worn or broken mechanical parts
• Evaluation and servicing of control panels, sensors, switches, and displays
• Testing and repair of electrical wiring, fuses, circuit boards, and power supplies
4. Functional System Testing
• Assessment of all major functions specific to the equipment type (e.g., speed, temperature, force, weight, timing)
• Operation of control interfaces, programming menus, and digital displays
• Verification of stabilization time, responsiveness, and user input reliability
5. Testing and Performance Verification
• Testing of internal sensors, controllers, and measurement systems using certified tools
• Multi-point testing to ensure repeatability, accuracy, and performance consistency
• Confirmation of user-defined setpoints, timing sequences, or programmable cycles
6. Safety and Compliance Checks
• Testing of safety interlocks, alarms, and over-limit protection systems (as applicable)
• Electrical safety inspections, including grounding and insulation verification
7. Final Quality Assurance and Documentation
• Full operational testing under simulated lab conditions
• Completion of performance benchmarks, testing results, and repair logs
• Final cleaning and visual inspection
Trust the Experts at American Instrument Exchange
With over 50 years of experience in the laboratory equipment industry, American Instrument Exchange is a trusted leader in high-quality refurbished lab instruments. Our refurbishment protocols ensure that every piece of equipment we sell is lab-ready—offering the precision, performance, and durability your team can count on.
Whether you’re outfitting a new lab or expanding an existing operation, choose American Instrument Exchange for tested, warrantied, and cost-effective laboratory equipment.
Warranty Information
All used equipment sold by American Instrument Exchange is refurbished/reconditioned, tested to meet specifications, cleaned, and comes with a 90-day warranty from the date of shipment unless otherwise specified. New products include a warranty from the manufacturer. Your warranty is only valid if you have paid your invoice. If your invoice is over 30 days old, warranty work will not be performed until your invoice is paid in full. American Instrument Exchange is not liable for any special or consequential damages that result from the use of, or the inability to use, the materials on this site or the performance of the products,
Exceptions include international sales and items that are agreed to be sold with a lesser warranty or items that are agreed to be sold “as is.”
Should there be visible shipping damage to packaging or concealed shipping damage to item(s) supplied, buyer must communicate such damage to the delivering entity or carrier upon receipt first and to American Instrument the same day item is accepted / signed for. Failure to do so voids warranty. Customer decision to involve / procure third party or OEM service other than American Instrument or AIE assigned vendors to resolve in-warranty instrument failure or defect without first placing a service call to American Instrument voids warranty.
Return & Cancellation Policy
American Instrument Exchange will authorize the return of and issue a full refund for any equipment that is not working as represented and could not be replaced or repaired to the customer’s satisfaction by AIE or a representative of AIE during the warranty period. Returns without prior authorization and an RMA number will not be accepted.
Customers are responsible for proper packaging of the equipment and all included accessories. American Instrument will pay for insurance and shipping costs. Non-inventory items bought specifically to fill customer orders may possibly be returned, but on a case by case basis.
Customers who cancel orders after refurbishing has begun or after delivery where there are no equipment performance issues may be subject to a Restocking/Cancellation Fee of 20% or more and responsible for shipping costs for both the delivery and return.
Ongoing and Extended Support Options
American Instrument Exchange is able to provide additional repair and support services outside the warranty terms for most products that sell.
For biosafety cabinets, clean benches, chemical fume hoods, and other clean air products our team at AIE Laboratory Services can provide certifications, repairs, decontaminations, and other services for customers throughout New England, and guidance and limited technical assistance for any customers in the US and Canada for new or refurbished biosafety cabinets purchased from American Instrument Exchange.
For all other products, the repair service team at American Instrument Exchange can provide both field and depot repair evaluations. We can easily schedule and coordinate the pick-up and transportation of your malfunctioning equipment. By offering hourly rates lower than most OEM service providers and eliminating travel time for technicians, we help reduce repair costs. Furthermore, our lab depot repair service minimizes or eliminates scheduling delays. Our experienced service technicians are qualified to restore your equipment to factory specifications.
Yes, all equipment from American Instrument Exchange comes with a warranty. Used/reconditioned/refurbished equipment is tested to make sure it operates to the manufacturer's specifications and comes with a 90-day warranty (unless otherwise noted). New equipment comes with a warranty from the manufacturer.
How do you test and recondition the equipment?
Testing requirements vary across all the equipment categories we sell. Temperature controlled units are tested with NIST traceable probes and data loggers. Gaskets, external housing, glass, handles, controls and control screens are all thoroughly inspected for integrity and functionality. We test all equipment using the manufacturer's parameters and specifications to confirm that the unit operates properly.
How do products ship from American Instrument Exchange?
We can ship products both nationally and internationally using a well-established network of transporters. Smaller items will ship via UPS. Larger equipment will be palletized and shipped either LTL or air-ride, depending on the specific equipment and/or delivery requirements.
Return and order cancellation policy
American Instrument Exchange will accept the return of any product that is not working as represented and could not be replaced or repaired to the customer's satisfaction during the warranty period. Customers who cancel orders after refurbishing has begun will be subject to a cancellation and restocking fee of between 20% and 40%.
Are discounts available for educational or non-profit institutions, or for bulk purchases?
Yes – call or email us today with a list of equipment you're looking for and we can potentially put together a quote that includes a discount.
How does your price matching policy work?
We strive to keep our pricing competitive and reasonable. If you find comparable items for sale at a lower price from other vendors please send us a link and or quote for the item and we'll do our best to match or beat the price.
Can I see the equipment in person before committing to a purchase?
Customers are welcome to make an appointment to view equipment in our warehouse. Given our workload we may not be able to test or clean the equipment prior to your arrival if you have not committed to an order.
1023 Western Avenue is a working warehouse, not a showroom, and customers should dress appropriately and wear closed toe shoes.
Can I ship products that I purchased elsewhere to American Instrument for repair?
Yes – please see our repair services page for more information.
