The Yoshitake GD-400 and GD-400SS are pilot-operated diaphragm pressure reducing valves designed for air and nitrogen gas applications. Featuring a pressure balance structure, these valves maintain a constant reduced pressure regardless of inlet pressure fluctuations. With a maximum pressure reduction ratio of 400:1 and a large pressure sensing area diaphragm, they offer highly accurate set pressure control over a wide range of operating conditions. The GD-400 features a cast iron body, while the GD-400SS is constructed from cast stainless steel (SCS14) for enhanced corrosion resistance.

Features

1. Pressure Balance Structure: Keeps the reduced pressure at a constant level without being affected by inlet pressure.
2. Simple Maintenance: Due to its simple structure, disassembly and maintenance can be conducted easily.
3. High Reduction Ratio: Wide range of use due to a high maximum pressure ratio of 400:1.
4. High Accuracy: A diaphragm with a large pressure sensing area provides accuracy to high set pressures.

Specifications

Model	GD-400	GD-400SS
Nominal size	15-50A	15-50A
Application	Air, Nitrogen gas *1	Air, Nitrogen gas *1
Inlet pressure	2.5-400 kPa	2.5-400 kPa
Reduced pressure	(A) 0.5-1.4 kPa (B) 1.2-3.3 kPa (C) 3.0-8.0 kPa (D) 7.0-20 kPa	(A) 0.5-1.4 kPa (B) 1.2-3.3 kPa (C) 3.0-8.0 kPa (D) 7.0-20 kPa
Working temperature	5-60°C *3	5-60°C *3
Minimum differential pressure	2.0 kPa	2.0 kPa
Maximum reduction ratio	400:1	400:1
Detection method	External sensing *2	External sensing *2
Min adjustable flow rate	15-25A: 1.2 m³/h (standard condition) 32-50A: 10.0 m³/h (standard condition)	15-25A: 1.2 m³/h (standard condition) 32-50A: 10.0 m³/h (standard condition)
Body Material	Cast iron	Cast stainless steel (SCS14)
Valve / Seat / Spindle	Stainless steel	Stainless steel
Disc / Diaphragm	NBR *3	NBR *3
Connection	JIS 10K FF Flanged	JIS 10K FF Flanged

Notes

*1 Please contact us when using for other fluids. *2 A conduit (φ8-2 m) and a joint for external sensing are included for GD-400. For GD-400SS, please prepare one at your end. *3 Available with FKM type (Operating temperature: 5~90 °C). Use on a compressed air system with dry air from oil-free compressors may cause deterioration of rubber parts in a very short time (ozone crack). Please consult with us before such installation.

Dimensions and Weights

Nominal size	L (mm)	H1 (mm)	H (mm)	Weight (kg)
15A	166	86	526	29.0 (32.0)
20A	170	86	526	29.0 (32.0)
25A	170	86	526	30.0 (33.0)
32A	180	96	561	32.0 (34.0)
40A	180	96	561	32.0 (34.0)
50A	180	101	561	33.0 (35.0)

The values in parentheses are the weights of the GD-400SS.

Characteristics

Flow Characteristic Chart

Pressure Characteristic Chart

This chart shows variation in reduced pressure when the inlet pressure of 400 kPa is changed to 10 kPa while the reduced pressure is set at 8.0 kPa.

Nominal Size Selection

When the inlet pressure is between 2.5 kPa and 200 kPa (Fluid: 20˚C Air)

Example: When selecting the nominal size of a pressure reducing valve whose inlet pressure (P1), reduced pressure (P2), and flow rate are 10 kPa, 3 kPa, and 15 m³/h (standard condition), respectively, first find the intersection point (a) of the inlet pressure of 10 kPa and the reduced pressure of 3 kPa. Trace down vertically from this intersection point to find intersection point (b) with the flow rate of 15 m³/h (standard condition). Since intersection point (b) lies between nominal sizes 20A and 25A, select the larger one, 25A. Set the safety factor at 80 to 90%.

Cv Values

Nominal Size	15A	20A	25A	32A	40A	50A
GD-400	1.5	2.0	3.0	5.0	6.0	8.0 [6.5]
GD-400SS	1.5	2.0	3.0	5.0	6.0 [5.5]	7.5 [6.0]

[ ] indicates FKM Type.

Installation and Piping

Installation Precautions

1. Connect the external sensing part to the outlet side.
2. Do not adjust the needle valve of the pressure reducing valve unreasonably.
3. Make sure to use a pipe with a diameter that can keep the inside flow velocity between 5 m/s and 15 m/s for the outlet side.
4. Install a strainer (equivalent to 80 mesh) to the inlet of the pressure reducing valve.
5. Connect a primary pressure regulating valve or safety valve to the outlet side to protect it and outlet side equipment.

Airtight Test Pressure

When performing a pressure test or airtight test after connection to the piping, apply the air test pressure specified below. If pressure beyond the specified air test pressure is applied, internal parts may be damaged.

Airtight test	Pressure
Inlet pressure	400 kPa or less
Reduced pressure (A)	1.8 kPa or less
Reduced pressure (B)	4.2 kPa or less
Reduced pressure (C)	10 kPa or less
Reduced pressure (D)	25 kPa or less

Maintenance and Troubleshooting

Be aware of foreign materials in the piping since many faults in the pressure reducing valve are caused by the existence of foreign objects. A clogged strainer will decrease the outlet pressure, and a leaking bypass pipe will increase the outlet pressure.

Periodic Replacement of Consumable Parts

Parts	Replacement interval
Diaphragm	3 years
Balance diaphragm	3 years
Disc	3 years
O-ring	3 years

Troubleshooting Guide

Problem	Presumable cause	Corrective action
I. Reduced pressure exceeds prescribed value.	1. Leakage from the stop valve on bypass pipe. 2. External sensing pipe tube is not connected. 3. Needle valve is clogged by foreign materials. 4. Foreign object pinched between disc and valve seat. Damage to disc and/or valve seat. 5. Loosened hexagon socket head cap bolt and/or locknut. 6. Damaged diaphragm. 7. Damaged balance diaphragm.	1. Close the stop valve. If leakage continues, replace the stop valve. 2. Connect the external sensing pipe. 3. Purge the foreign materials from needle valve. 4. Remove the foreign object. Replace the disc if damaged. If the seat is damaged, consult us. 5. Tighten hexagon socket head bolt and locknut. 6. Replace diaphragm. 7. Replace balance diaphragm.
II. Reduced pressure does not reach prescribed value. Or, fluid fails to flow.	1. Strainer at inlet is clogged. 2. Needle valve is clogged by foreign materials. 3. Foreign object pinched between diaphragm shell and slide of top guide.	1. Clean the screen of the strainer. 2. Remove foreign material from needle valve. 3. Remove foreign objects from diaphragm shell and slide of top guide.
III. External leakage	1. Needle valve is clogged by foreign materials. 2. Loosened hexagon head bolt of bottom cover, or damaged O-ring. 3. Loosened hexagon head bolt on top diaphragm case. 4. Damaged diaphragm.	1. Remove foreign material from needle valve. 2. Tighten hexagon head bolt on bottom cover or replace O-ring. 3. Tighten hexagon head bolt on top diaphragm case. 4. Replace diaphragm.

Exploded View and Parts List

No.	Name of Parts	Material	No.	Name of Parts	Material
1	Body	Cast Iron	23	Top Dia. Plate	Carbon Steel
2	Valve Seat	Stainless Steel	24	Washer	Steel
3	O Ring	NBR	25	Nut	Stainless Steel
4	O Ring	NBR	26	Bolt	Stainless Steel
5	Bottom Dia. Case	Cast Iron	27	Top Dia. Case	Cast Iron
6	Bolt	Stainless Steel	28	Bolt	Steel
7	Balance Diaphragm	NBR	29	Spring	Piano Wire
8	Top Guide	Stainless Steel	30	Spring Plate	Cast Iron
9	Bolt	Stainless Steel	31	Spring Chamber	Cast Iron
10	Disc	NBR	32	Bolt	Steel
11	Valve	Stainless Steel	33	Lock Nut	Steel
12	Spindle	Stainless Steel	34	Adjusting Screw	Brass
13	Spring Washer	Stainless Steel	35	Cap	Cast Iron
14	Nut	Stainless Steel	36	O Ring	NBR
15	Spring	Stainless Steel	37	Needle Valve	Stainless Steel
16	Bottom Guide	Stainless Steel	38	Name Plate	Stainless Steel
17	Bottom Cover	Cast Iron	40	Stud Bolt	Steel
18	Bolt	Steel	41	Nut	Steel
19	Diaphragm Shell	Stainless Steel	42	Eye Nut	Steel
20	O Ring	NBR	43	Sensing Pipe	Copper
21	Bottom Dia. Plate	Stainless Steel	44	Joint	Brass
22	Diaphragm	NBR