Yoshitake GD-21 is a direct type, diaphragm-operated differential pressure regulating valve designed for cold and hot water applications. It is highly suitable for use as a relief valve for pumps in closed circuits. Featuring a single seat valve and valve disc, the GD-21 ensures no leakage when closed. The valve features a ductile cast iron body and operates within a temperature range of 5 to 80°C.

Features

• Most suitable for relief valve of a pump in closed circuit.
• No leakage when closed due to single seat valve and valve disc.

Specifications

Application	Cold and hot water
Regulating differential pressure	15A-80A: (A) 0.05-0.25 MPa, (B) 0.26-0.7 MPa 100A-150A: (A) 0.05-0.25 MPa, (B) 0.26-0.5 MPa
Fluid temperature	5-80°C
Material (Body)	Ductile cast iron
Material (Valve seat)	Stainless steel or bronze
Material (Valve disc)	NBR
Material (Diaphragm)	NBR
Connection	JIS 10K FF flanged
Inside surface treatment of body	15A-100A: Electrodeposition coating 125A-150A: Tar-based coating (black) or Electrodeposition coating

Caution

Please confirm that the indications on the product correspond with the specifications of the ordered model before use. If they are different, do not use the product and contact us.

Dimensions (mm) and Weights (kg)

Nominal size	L	H	$H_1$	d	Weight
15A	145	298	57	36	8.3
20A	150	298	57	36	8.3
25A	150	320	67	36	10.1
32A	195	400	76	48	17.4
40A	195	400	76	48	17.4
50A	195	414	81	48	19.3
65A	270	572	110	63	40.1
80A	270	597	125	63	43.8
100A	308	665	143	68	70.1
125A	380	874	179	115	144.1
150A	400	929	204	115	173.1

The material shapes are slightly different depending on the nominal size.

Piping Example

TIP

Install a needle valve to the outlet side of the product and plumb it to the pressure sensing pipe using copper piping.

Flow Characteristic Chart

Set range MPa	Accumulation MPa
0.05-0.25	Within 0.05
0.26-0.7	Within 0.105

Nominal Size Selection

Nominal Size Selection Chart (For Liquid)

Example: When selecting the nominal size of a differential pressure regulating valve whose differential pressure (ΔP), specific gravity, and flow rate (V) are 0.2 MPa, 1 (water), and 5.5 m³/h, respectively, first trace down vertically from the differential pressure (ΔP) of 0.2 MPa to find intersection point (a) with the flow rate (V) of 5.5 m³/h. Since this intersection point (a) lies between nominal sizes 25A and 32A, select the larger one, 32A.

When the specific gravity is 0.7 under the same conditions, trace down vertically from the differential pressure (ΔP) of 0.2 MPa to find intersection point (b) with the specific gravity 1. Find intersection point (c) with the specific gravity of 0.7 by tracing horizontally to the slant lines from this intersection point (b). Then, find intersection point (d) with the flow rate (V) of 5.5 m³/h by tracing down vertically from intersection point (c). Since this intersection point (d) lies between nominal sizes 20A and 25A, select the larger one, 25A.

Calculation Formula for Cv Value

Nominal size	15A	20A	25A	32A	40A	50A	65A	80A	100A	125A	150A
Cv value	1.5	2.7	4	8.5	11	14	23	32.5	48	75	108

$$ \mathbf {C v} = \frac {\mathbf {0 . 3 6 5 V} \sqrt {\mathbf {G}}}{\sqrt {\Delta \mathbf {P}}} $$

• P1: Inlet pressure
• P2: Outlet pressure
• ΔP: P1 - P2
• G: Specific gravity (relative to water)
• V: Max. liquid flow rate [m³/h]
• Cv: Cv value of each nominal size

INFO

(1) Joint for the outlet pressure sensing is not included with the product package. (2) Secure the required space for maintenance and inspection.

Installation

Precautions for Installation

Caution

1. As the product is heavy, support it securely by lifting device while installation. Failure to follow this notice may result in bodily injury due to a drop accident.
2. Do not disassemble the product unless it is necessary.
3. Be sure to remove foreign substances and scales from the piping before connecting the product.
4. Install the product vertically to the horizontal piping. If installing it to a vertical piping is inevitable due to limited space, the product can be installed to the vertical piping as long as its size is less than 100A. Do not install the product of 100A or larger to a vertical piping.
5. Be sure to install pressure gauges to both the inlet and outlet sides of the product. In addition, install strainer and bypass line to the piping around the product.
6. Be sure to install a strainer (60-80 mesh) at the inlet side of the product.
7. Quick operating valve shall be installed more than 3 meters away from the product.
8. Do not apply excessive load, torque or vibration to the valve when piping.
9. Place a drain pipe between the stop valve and the product for easier maintenance and inspections.

Space Required for Disassembly (mm)

Nominal size	15A	20A	25A	32A	40A	50A	65A	80A	100A	125A	150A
$H_2$	500	500	500	650	650	650	800	800	1000	1200	1400

Operating Procedure

Precautions for Operation

Caution

1. Before leading fluid into the product, close the stop valves before and after the product and remove all foreign substances or scales via the bypass line.
2. Before leaving the product not operated for a long time, discharge the fluid inside of the product and piping completely, and close the stop valves before and after the product. The fluid can be drained out of the product efficiently with the air vent valve.
3. Pressure regulation of the product shall be performed while the fluid running. To increase the set differential pressure, loosen the lock nut, and then slowly turn the adjusting screw clockwise. To decrease the set differential pressure, slowly turn the adjusting screw counterclockwise.
4. Remove air accumulated in top and bottom sides of diaphragm using the air vents.

Precautions for Air Vent

Warning

Do not stand in front of the air vent valve during use. Failure to follow this notice may result in scalds or bodily injury due to blow-off of the fluid inside.

Caution

Do not rotate the air vents more than 1/2 turn when use. Failure to follow this notice may make the air vents detached from the body. In this case, the air vents may not be reattached.

How to Use Air Vent

1. Rotate the screw of the air vent counterclockwise to loosen it order to discharge air.
2. Rotate the screw of the air vent clockwise to the original closed position after discharging air.

Maintenance

Precautions for Disassembly and Maintenance

Warning

1. Disassembling and inspections must be performed by experienced professional or valve manufacturer.
2. Before disassembly or inspection, completely release internal pressure of the product, piping and equipment. When the fluid is hot, cool down the product to the condition that it can be touched with bare hands.

Disassembly

1. Release the internal pressure from the piping completely, and make sure that the pressure gauge shows that the pressure is zero.
2. Remove the cap and slightly loosen the lock nut, and then turn the adjusting screw counterclockwise so that the adjusting spring can be in no load condition.
3. Remove the spring chamber by unscrewing the bolt, and then take out the adjusting spring and the spring plate.
4. Remove the diaphragm by fixing the spindle and loosening the U nut.
5. To remove the retainer, loosen the bolt and pull out the retainer guide together with the retainer.

Nominal size 15-50A To remove the retainer guide easily, reattach the spring plate and U nut to the spindle, then pull up the spring plate.

Nominal size 65-150A To remove the retainer guide easily, screw the bolt to the retainer guide and pull them out.

Reassembly

To reassemble the product, take reverse procedure to disassembly.

Caution

1. Make sure that there are no flaws on the diaphragm, the valve seat and the valve.
2. Apply silicon grease to the O-ring after confirming that there are no flaws on it.
3. Confirm that the lip of the diaphragm is fitted in the grooves on the body, and then attach the spring chamber.
4. There should be a gap between the retainer guide and the body when properly assembled. Tighten the bolts evenly to avoid over-tightening them.

Troubleshooting

Trouble	Cause	Remedy
Excessive leakage Adjustment is impossible.	1. Foreign substances stuck between valve and valve seat. Or damage on valve and/or valve seat. 2. Damage on diaphragm and/or O-ring. 3. Nominal size is too small for the specifications. 4. Pressure gauge is out of order.	1. Disassemble and clean, or replace. 2. Replace diaphragm and/or O-ring. 3. Replace the product to obtain proper nominal size. 4. Replace.
Abnormal sound is observed	1. Air-induced problem occurs. 2. Nominal size is too large for the specifications.	1. Install exhaust equipment. 2. Replace the product to obtain proper nominal size.