Yoshitake OB-31U is a direct-acting temperature regulator designed for cooling applications. Featuring a single valve and balanced bellows structure with a soft PTFE valve seat, it provides excellent durability and stable temperature control without being affected by inlet pressure fluctuations. The regulator is widely used for cold water and refrigerants, equipped with union joint connections for easy installation.

The regulator consists of a bronze body and a separate thermal bulb sensor. The sensor, equipped with a 2-meter standard copper capillary tube, can be easily attached or detached from the body, allowing for simple thermal specification changes. Operating by sensing the fluid temperature, the bellows expands to open the valve as the temperature rises, and a spring closes the valve as the temperature falls, maintaining precise temperature regulation.

Features

• The blue handle indicates the cooling type, making it easy to identify its application at a glance.
• Excellent durability and high sealability are ensured by the stainless steel and fluororesin (PTFE) valve components.
• The single valve and balance bellows structure offers stable temperature control without being affected by inlet pressure fluctuations.
• Easy attachment and detachment of the body and thermal bulb allow for simple thermal specification changes.
• The initial temperature is easily set by operating the handle.

Specifications

Body

Model	OB-31U
Purpose	For cooling
Application	Cold water, Refrigerant
Maximum pressure	1.7 MPa
Max. differential pressure	1.0 MPa
Valve seat leakage	0.05% or less of rated flow rate
Max. temperature	185°C
Material (Body)	Bronze
Material (Valve disc)	Brass (PTFE)
Material (Valve seat)	Stainless steel
Connection	JIS Rc screwed (union joint)

Sensor

| Cooled fluid | Cold and hot water, Oil, Liquid | | Maximum pressure | 1.0 MPa | | Material (Thermal bulb) | Copper pipe (nickel chrome plated) * | | Material (Capillary) | Copper pipe | | Material (Capillary tube) | Stainless steel | | Standard capillary length | 2m | | Connection | JIS R 1/2 |

• Available with thermal well (stainless steel). Available with capillary lengths of 3 or 5 meters.

Temperature Adjusting Range

Temperature adjusting range (°C)	Withstand temperature (°C)
0-35	75
25-70	110
40-100	140

The maximum temperature of the thermal bulb for cooling is 100°C.The term "withstand temperature" means the temperature from pressure resistance of the bellows.

Dimensions and Weights

Nominal Size	d	L (mm)	Weight (kg)
15A	Rc 1/2	160	3.1
20A	Rc 3/4	160	3.1
25A	Rc 1	160	3.1

Note: The sensor weight is 0.6 kg.

Nominal Size Selection (For Water)

How to use the chart

When selecting the nominal size of a temperature regulator whose inlet pressure, outlet pressure, and flow rate are 0.3 MPa, 0.15 MPa, and 1 m³/h, respectively, first find intersection point (a) of the differential pressure (ΔP) of 0.15 MPa (0.3 MPa – 0.15 MPa) before and after the valve and the flow rate of 1 m³/h. Since this intersection point (a) lies between nominal sizes 15A and 20A, select the larger one, 20A. (Chart of the flow rate is a reference value).

Structure and Operation

Heating the thermal bulb makes its inner pressure rise, while cooling it makes the pressure lower. The bellows expands or contracts responding to the change in internal pressure that is transmitted through the capillary tube, and this allows the valve to open or close.

For the OB-31U cooling regulator, when the temperature of the thermal bulb rises, the bellows expands and applies a lifting force to the spindle to open the valve. When the temperature of the bulb lowers, the downward force applied to the spindle by the spring closes the valve. The set temperature can be adjusted by turning the handle to change the load of the spring.

Installation and Piping

Installation Precautions

• Be sure to install a strainer (60 to 80 mesh) at the inlet side of the product.
• Be sure to install pressure gauges at the inlet and outlet sides of the product for operation checks.
• Make sure that more than 3/4 of the thermal bulb's total length is in direct contact with the fluid to be cooled.
• The bend radius of the capillary tube should be more than 40 mm. Avoid bending at a sharp angle, twisting, or pulling it with force.
• Adjust the set temperature while watching the thermometer with enough time.