Danfoss AVTA Thermostatic Water Valve

Overview

The Danfoss AVTA is a self-acting thermostatic water valve that regulates the flow of cooling water in proportion to the temperature at its sensor. It needs no electrical supply or compressed air: a sealed thermostatic element opens the valve as the sensor temperature rises and closes it as the temperature falls, holding the machine or process at a constant temperature without wasting cooling water. The Danfoss AVTA is available in sizes from G⅜ to G1, in brass or in stainless steel for aggressive media, with three types of sensor charge for different installation conditions.

Seven Star LLC supplies the Danfoss AVTA to maintenance teams, OEMs and contractors in the Sultanate of Oman and across the GCC, with engineering support in Muscat. In a region where cooling water is often desalinated or brackish and costly, a simple self-acting valve that admits only the water actually needed is a practical way to reduce consumption.

Working Principle

The Danfoss AVTA consists of three main elements: a setting section with knob, reference spring and scale; a valve body with orifice, closing cone and seals; and a hermetically sealed thermostatic element with sensor, capillary tube, bellows and charge. When the sensor temperature changes, the pressure of the charge changes and is transmitted through the capillary to the bellows, where it acts against the setting spring. When the two forces balance, the spindle stays still; when the temperature or the setting changes, the spindle moves until balance is restored.

The result is proportional control, with flow change roughly proportional to the change in sensor temperature. Because the valve is pressure-relieved, its degree of opening is not affected by the differential pressure across it, which makes the Danfoss AVTA insensitive to supply pressure variations. Danfoss also describes it as insensitive to dirt, and it accepts ethylene glycol mixtures up to 40 % as cooling medium.

Engineering Design of the Danfoss AVTA

Three sensor charges are offered. The adsorption charge, active carbon and CO2, uses a small ø9.5 × 150 mm sensor and can be installed in any position regardless of orientation or relative temperature. The universal charge uses a ø18 × 210 mm sensor that may be colder or warmer than the valve, and the mass charge uses a ø9.5 × 180 mm sensor with a short time constant, which must sit in a place warmer than the valve. All sensors withstand 25 bar, and immersion pockets in brass or stainless steel are available.

In the brass version the valve body is forged brass with a brass spindle, while the Danfoss AVTA SS version uses stainless steel for the body, spindle and other metal parts; both have a stainless steel seat, NBR valve cone, EPDM diaphragms and a copper sensor. Valves measure 240 mm high and weigh 1.45 to 1.65 kg. Maximum working pressure is 16 bar, test pressure 25 bar, and differential pressure 0 to 10 bar.

Ordering is straightforward because each code number covers the complete valve including the capillary tube gland. Capillary lengths of 2, 2.3 and 5 m are listed, several sizes come with an armoured capillary for exposed locations, and one AVTA 25 variant has a ø2 mm bypass drilled in the body so that a small flow continues when the valve is closed. Accessories include a mounting bracket, heat-conductive compound for sensor pockets, NBR diaphragm sets for mineral oil, capillary glands in G and NPT threads and a plastic hand knob, while thermostatic elements are available as spare parts.

Key Features

The valve offers the following practical advantages:

• Fully self-acting operation with no electrical supply or compressed air required.
• Opens on rising sensor temperature for proportional cooling water control.
• Pressure-relieved design keeps the opening independent of differential pressure.
• Insensitive to dirt and to supply pressure variations.
• Adsorption, universal and mass charges suit almost any sensor location.
• Stainless steel AVTA SS version for aggressive media in the marine sector and chemical industry.
• Regulating ranges of 0–30, 25–65, 50–90 and 10–80 °C depending on charge.
• Kv values from 1.4 to 5.5 m³/h at 1 bar across sizes AVTA 10 to AVTA 25.

Industrial Applications

Danfoss lists injection moulding machines, compressors, vacuum pumps, dry cleaning machines, distillation plants, printing machines, hydraulic systems, roller mills, biomass boilers, industrial lasers, steam sterilisers, medical equipment and food processing as typical uses for the Danfoss AVTA. In Oman this translates to cooling water on air and gas compressor oil coolers, hydraulic power unit heat exchangers, plastics and packaging plants in Rusayl and Sohar, laboratory and hospital sterilisers, and process coolers in food and beverage factories. The valve can be installed in either the supply or return line.

Where electrical on/off control is preferred, a solenoid valve such as the Danfoss EVR 25 solenoid valve can switch the flow, while the Danfoss AVTA gives continuous proportional control without wiring. Cooling circuit pressure can be monitored with the Danfoss MBS 3000 pressure transmitter, and industrial refrigeration plants on the same site often use the Danfoss ICV control valve.

For water, oil and air lines needing a servo-operated on/off valve, see the Danfoss EV220B 15-50 solenoid valve.

Technical Specifications

The Danfoss AVTA data below come from the current Danfoss data sheet.

How to Order

Send Seven Star LLC the cooling water flow, required temperature, sensor location and connection size, and we will recommend the Danfoss AVTA size, charge and capillary length. Our Muscat team advises on stock and delivery across Oman and the GCC and can provide the official Danfoss AVTA data sheet and immersion pocket options with your quotation.