Yoshitake OB-31 and OB-31U are direct-acting type bellows soft seat temperature regulators designed for cooling applications using cold water or refrigerant. The OB-31 features a JIS Rc screwed connection, while the OB-31U uses a union joint. The series also includes the OB-30 and OB-30U, which are designed for heating applications using steam or hot water. These regulators feature a single valve and balance bellows structure that offers stable temperature control without being affected by inlet pressure fluctuations. The valve parts are constructed of stainless steel and fluororesin, ensuring excellent durability and high sealability.

Features

• Easy identification: Blue handle type is for cooling (OB-31, OB-31U), and red handle type is for heating (OB-30, OB-30U).
• Excellent durability and sealability: Ensured by valve parts made of stainless steel and fluororesin.
• Stable temperature control: Single valve and balance bellows structure operates without being affected by inlet pressure fluctuations.
• Easy maintenance: Easily changeable thermal specification by easy attachment and detachment of the body and thermal bulb.
• Wide adjustment range: Applicable to a wide variety of applications.
• Common thermal bulb: The thermal bulb is usable for both heating and cooling, common for all sizes (15A to 25A).
• Simple setting: Easy setting of the initial temperature by handle operation.

Specifications

Body Specifications

Model	OB-31 / OB-31U	OB-30 / OB-30U
Purpose	For cooling	For heating
Application	Cold water, Refrigerant	Steam, Hot water
Maximum Pressure	1.7 MPa	1.0 MPa (1.7 MPa for hot water)
Max. Differential Pressure	1.0 MPa	1.0 MPa
Valve Seat Leakage	0.05% or less of rated flow rate	0.05% or less of rated flow rate
Max. Temperature	185 °C	185 °C
Material (Body)	Bronze	Bronze
Material (Valve)	Brass (PTFE)	Brass (PTFE)
Material (Valve Seat)	Stainless steel	Stainless steel
Connection	JIS Rc screwed (OB-31) / JIS Rc screwed with union joint (OB-31U)	JIS Rc screwed (OB-30) / JIS Rc screwed with union joint (OB-30U)

Sensor Specifications

| Heated Fluid | Cold and hot water, Oil, Liquid | | Cooled Fluid | Cold and hot water, Oil, Liquid | | Maximum Pressure | 1.0 MPa | | Material (Thermal Bulb) | Copper pipe (Nickel chrome plated) * | | Material (Capillary Tube) | Copper pipe | | Material (Flexible Tube) | Stainless steel | | Standard Capillary Length | 2 m (Optional 3 m or 5 m available) | | Connection | JIS R 1/2 screwed |

*Available with a thermal well (stainless steel).

Temperature Adjusting Range

Temperature Adjusting Range (°C)	Withstand Temperature (°C)
0–35	75
25–70	110
40–100	140
60–130	170
70–150	190

Note: 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

OB-31 Body Dimensions

Nominal Size	d	L (mm)	Weight (kg)
15A	Rc 1/2	75	2.1
20A	Rc 3/4	80	2.2
25A	Rc 1	90	2.4

OB-31U Body Dimensions

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

Sensor Dimensions

Capillary Length	Weight
2 m	0.6 kg

Structure and Parts

No.	Part Name	No.	Part Name
1	Body	12	Handle
2	Spring chamber	13	Bellows follower
3	Disc	14	Bellows
4	Valve	15	Ring
5	Valve seat	16	Gasket
6	Balance bellows	17	Bolt
7	Spindle	18	Bushing
8	Nut	19	Washer of packing
9	Guide	20	Thermal bulb
10	Guide	21	Capillary tube
11	Spring	22	Packing

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 the internal pressure that is transmitted through the capillary tube, and this allows the valve to open or close. For the OB-31 and OB-31U (cooling), when the temperature of the thermal bulb rises, the bellows expands and applies lifting force to the spindle to open the valve. When the temperature 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.

Nominal Size Selection

OB-31 / OB-31U Size Selection Chart (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:

1. 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.
2. Since this intersection point (a) lies between nominal sizes 15A and 20A, select the larger one, 20A.

Installation

Precaution for Installation

WARNING

• Be sure to remove foreign substances and scale from the piping before connecting the product.
• Be sure to install a strainer (60 to 80 mesh) at the inlet side of the product.
• Install pressure gauges at the inlet and outlet sides of the product for operation checks.
• Check the direction and posture of the product so that the fluid flowing and the arrow marked on the body are in the same direction.
• Install the product in a place where the ambient temperature does not exceed the set temperature.
• Install a thermometer close to the thermal bulb.
• 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.

Assembly of Body and Sensor

Place the bellows follower, which is packaged with the body, into the bellows with its flat surface facing downward and then screw it into the lower surface of the body by the ring. It makes the assembly easier to loosen the handle in the direction of the “L” position. Be sure not to lose the bellows follower because the product does not function properly without it.

Piping Example for Cooling

Operating Procedure

1. Close the stop valves at the inlet and outlet sides of the product. Open the bypass stop valve and blow fluid through the bypass line with enough time. After discharging, be sure to close the bypass stop valve.
2. Turn the handle and move the indicator to the desired temperature position on the scale. To raise the temperature, turn the handle clockwise (to the direction of the “H” position). To lower the temperature, turn it counterclockwise (to the direction of the “L” position).
3. Slowly open the inlet stop valve to its full open position, and then open the outlet stop valve little by little to its full open position.
4. Adjust the handle until the desired temperature is obtained while watching the thermometer.

OB-31, OB-31U Scale Reading and Set Temperature

Scale Reading	0–35 °C	25–70 °C	40–100 °C
0	-	-	-
1	-14 °C	11 °C	23 °C
2	9 °C	38 °C	55 °C
3	32 °C	65 °C	94 °C
4	55 °C	98 °C	141 °C

Note: The table shows the set temperature per scale reading as a guide. Because the temperature varies slightly according to conditions of use, adjust the handle until the desired temperature is obtained.

Maintenance and Troubleshooting

Temperature does not lower or lowers excessively:

• Inadequate adjustment: Readjust the handle.
• Thermal bulb or bellows damaged: Replace the sensor.
• Foreign substances stuck or damage on the disc and valve seat: Remove substances; replace parts if damaged.

Large error of temperature control:

• Thermal bulb and thermometer are in wrong positions: Reinstall them at points where the circulation is best.
• Inlet pressure is too high: When steam/water consumption is small, lower the inlet pressure.

Outside leakage:

• Leakage from the gasket: Retighten the gasket or replace the part.
• Balance bellows is damaged: Replace the part.

DANGER

Inspection must be done by an experienced professional or valve manufacturer. Completely discharge the pressure inside of the product, piping, and equipment prior to disassembly and inspection. When the fluid is hot, cool down the product to the condition that it can be touched with bare hands.