Yoshitake GD-28S-NE and GD-29S-NE are pressure reducing valves designed for cold and hot water applications. They feature an SCS13 body, FKM valve disc, and EPDM diaphragm, ensuring reliable performance up to a maximum temperature of 90°C and an inlet pressure of up to 2.0 MPa. The series offers reduced pressure ranges from 0.20 to 0.70 MPa.

The GD-28S-NE is available in nominal sizes from 20A to 50A with JIS Rc screwed connections, while the GD-29S-NE covers sizes from 20A to 100A with JIS 20K RF flanged connections. Models in sizes 20A to 50A incorporate a 40 mesh strainer.

Specifications

Model	GD-28S-NE	GD-29S-NE
Nominal size	20A-50A	20A-100A
Application	Cold and hot water	Cold and hot water
Inlet pressure	2.0 MPa or less	2.0 MPa or less
Reduced pressure A	0.20 - 0.35 MPa	0.20 - 0.35 MPa
Reduced pressure B	0.30 - 0.70 MPa	0.30 - 0.70 MPa
Min. differential pressure	0.05 MPa	0.05 MPa
Max. temperature	90°C	90°C
Body	SCS13	SCS13
Valve seat	SCS13	SCS13
Valve disc	FKM	FKM
Diaphragm	EPDM	EPDM
Connection	JIS Rc screwed	JIS 20K RF flanged

INFO

• Pressure gauge connection port is JIS R1/4. The maximum temperature of the pressure gauge is 45°C. If the fluid temperature exceeds 45°C, please protect the pressure gauge by using a siphon tube or similar.
• All the above models conform to the standard of the Japanese Water Supply Act.

Controllable Range

It can be used under the condition that the maximum decompression ratio is 7:1 within the controllable range shown in the figure below. If it is out of control, choose two-step decompression or another model. When the primary side pressure is 2.0 MPa, use it so that the secondary side pressure is 0.3 MPa or more.

Nominal Size Selection

If the pressure difference before and after the product is 0.15 MPa or more, choose the nominal size from the rated flow table below.

Rated flow table (The pressure difference before and after the product is 0.15 MPa or more)

Nominal size	15A	20A	25A	32A	40A	50A	65A	80A	100A
Rated flow (L/min)	30	40	60	100	150	240	300	450	700

If the pressure difference before and after the product is less than 0.15 MPa, choose the nominal size from the nominal size selection charts below.

Nominal size selection chart Nominal size 20A - 50A

Nominal size selection chart Nominal size 65A - 100A

Flow Rate Characteristics

Nominal size	Pressure range	Reduced pressure range	Offset
20A-100A	A	0.20-0.35 MPa	0.10 MPa or less
20A-100A	B	0.30-0.70 MPa	0.15 MPa or less
(Differential pressure after valve seat 0.15 MPa or more)

Pressure Characteristics

This chart shows variation in the reduced pressure when the inlet pressure of 1.0 MPa is changed between 0.35 MPa and 2.0 MPa after the reduced pressure is set at 0.30 MPa.

Noise Characteristics

(Fluid: Water. Nominal size 32A - 50A. Inlet pressure: 2.0 MPa, Reduced pressure: 0.3 MPa)

Operation

The spring is compressed by the adjusting screw, the diaphragm is pushed down, and thereby the disc directly connected to it is opened. Fluid coming in from the inlet side flows out from the upper part of the disc to the outlet side, and passes through the reduced pressure detection hole, and is led to the bottom of the diaphragm. The load of the spring and the reduced pressure act on the diaphragm, and the upper and lower force keeps a balance and regulates the valve opening. As a result, the diaphragm keeps the reduced pressure constant.

Installation

Piping Example

• Install a strainer on the inlet side of the pressure reducing valve of the nominal size 65A to 100A.
• Install same diameter 3m pipes on both the primary and secondary sides of the pressure reducing valve.

WARNING

• Before installing the product in the piping, be sure to remove foreign substances and scale from the piping.
• Be sure to install a strainer at the inlet side of the product of nominal size 65A to 100A. It is recommended to use a strainer of 40 mesh or more.
• Install a safety relief valve for equipment protection at the outlet side of the product.
• Be sure to install pressure gauges at the inlet and outlet sides of the product.

Adjusting Procedure

1. Close the stop valves at the inlet and outlet sides of the reducing valve, and take adequate time to blow out fluid by using a bypass line. In doing this, adjust the opening of the globe valve in the bypass pipe so as not to blow out the safety relief valve. After the end of blowing, close the globe valve without fail.
2. Fully open the stop valve at the inlet side slowly, and open the stop valve at the outlet side so that a little fluid can flow through.
3. Remove the domed cap nut and turn the adjusting screw while watching the pressure gauge at the outlet side.
   • Turn the adjusting screw to the right (clockwise) to increase the reduced pressure.
   • Turn the adjusting screw to the left (counterclockwise) to decrease the reduced pressure.
4. Fully open the stop valve at the outlet side slowly.
5. After the adjustment is complete, tighten the domed cap nut.

Maintenance

Most problems with the pressure reducing valve are caused by foreign substances and scale in the piping. Avoid the ingress of dust and dirt to the product with caution.

Troubleshooting

Trouble	Cause	Remedy
Abnormal pressure rise at the outlet side	1. Foreign substances stuck between the disc and the valve seat, or scratch on them. 2. The O-ring is damaged. 3. The diaphragm is damaged. 4. There is a leakage from the globe valve of the by-pass line.	1. Disassemble the product and remove the foreign substances. If scratch is observed on the valve disc or valve seat, replace it. 2. Replace the O-ring. 3. Replace the diaphragm. 4. Repair or replace the globe valve.
Reduced pressure does not reach the desired value	1. The working pressure is improper. 2. The nominal size of the product is too small for the flow rate for use. 3. Pressure adjustment is improper. 4. Strainer built in the product is clogged. 5. The strainer installed at the inlet side of the product is clogged.	1. Correct the working pressure. 2. Replace the product with the proper nominal size. 3. Readjust the pressure in accordance with the given procedure. 4. Clean the strainer. 5. Clean the strainer.
Outside leakage	1. Bolt is loosened. 2. O-ring is damaged. 3. Strainer cap or plug is loosened.	1. Tighten the bolts. 2. Replace the O-ring. 3. Tighten the strainer cap or plug.

TIP

Replacement intervals:

• Three years: Diaphragm, O-ring, Disc
• Five years: Other O-rings, seal washer

Strainer Cleaning Procedure

Clean the strainer regularly at least once or twice a year.

1. Close the stop valve at the inlet side and open the stop valve at the end, and remove the internal pressure from the product completely.
2. Turn the strainer cap counterclockwise, and remove it.
3. Remove the strainer from the strainer cap, and wash it in water, and remove deposited scale.
4. After cleaning, reinstall the strainer and strainer cap in the body.
5. Open the stop valve at the inlet side, and check that there is no leakage from the strainer cap. When there is a leakage, replace the O-ring.
6. Open the stop valve at the end, and check that the product operates normally.

Exploded View

Nominal size 20A - 50A:

Nominal size 65A - 100A: