Hydraulic Control Valve Guide

Pressure Reducing Valve Guide: 500X Hydraulic PRV & Water Supply Control Valves

In short: a hydraulic pressure reducing valve is a self-operated, pilot-controlled valve that holds a steady downstream pressure using only line pressure — no electricity. For water supply networks you typically choose between a 500X pressure reducing valve (constant downstream pressure), an F745X level control valve (constant tank level) and a 100X remote float valve (compact stainless steel option). This guide explains how each works and how to specify them.

500X Hydraulic Pressure Reducing Valve

DN20-DN600, 0.1-1.6 MPa adjustable

F745X Hydraulic Level Control Valve

DN50-DN400 float pilot, tank level control

100X-16P Remote Float Valve (CF8)

Stainless steel, DN40-DN300, 0-1.0 MPa

GKZF-1 Solenoid Control Gate Valve

DN50-DN300, AC220V/DC24V, 300 PSI

1. What Is a Hydraulic Pressure Reducing Valve?

A hydraulic pressure reducing valve (PRV) is a self-operated control valve that reduces a higher, fluctuating inlet pressure to a steady lower downstream pressure. It is called hydraulic because the valve is driven entirely by the pipeline pressure through a pilot system — there is no solenoid, motor or control cabinet involved. That makes it a low-cost, high-reliability building block for water supply zones, booster stations, irrigation networks and process water lines.

The classic example is the 500X hydraulic adjustable pressure reducing valve: a ductile iron (QT450-10) main valve with a forged brass pilot, covering DN20-DN600 with downstream pressure adjustable from 0.1 MPa to 1.6 MPa. The main valve body is available at 1.0 MPa, 1.6 MPa or 2.5 MPa nominal pressure, and the design conforms to ANSI, JIS and GB standards.

The diaphragm assembly is nylon-reinforced EPDM and the internal stem is stainless steel 304, with copper or stainless steel pilot tubing — the material choices that determine whether a PRV still holds its set point after years of duty.

2. How a Self-Operated 500X PRV Works

The 500X is a diaphragm-type globe valve with an adjustable pilot mounted on top. The pilot continuously senses the downstream pressure through a sensing line. When downstream pressure rises above the set point, the pilot throttles closed, pressure builds in the diaphragm chamber and the main valve moves toward closed. When downstream pressure falls below the set point, the pilot opens further, the chamber vents and the main valve opens wider. The valve therefore modulates continuously to hold the set pressure regardless of flow or inlet pressure variation.

Because the valve is completely self-operated, it keeps regulating even during a power failure — an important property for fire water and municipal networks where a pressure loss could be critical. The smooth, slow-closing characteristic also avoids high pressure surges and water hammer when flow stops, which is why hydraulic control valves are frequently preferred over fast-acting electric valves on large mains.

For projects where remote electric control is genuinely required rather than continuous modulation, a solenoid-operated unit such as the GKZF-1 grooved solenoid control gate valve (AC220V/DC24V, DN50-DN300, 300 PSI) provides automatic open/close on command while the PRV handles steady pressure control.

3. PRV vs Level Control vs Float Valve

Hydraulic control valves share the same self-operated pilot principle but regulate different process variables. The table below compares the three most common duties in water supply.

If your project needs pressure regulation plus tank filling, the standard architecture is a 500X PRV on the supply line feeding an F745X or 100X float valve at the tank inlet — each valve doing the duty it is designed for.

4. Where Each Valve Belongs

Pressure reducing (500X): anywhere a high-pressure main feeds a lower-pressure zone — district metered areas, high-rise booster discharge, irrigation headers and process water. Set the downstream pressure once and the valve holds it across the daily demand curve.

Level control (F745X): the F745X hydraulic water level control valve automatically maintains a preset level in reservoirs, water tanks and water towers using a float pilot, preventing overflow and extremely low levels. It is driven entirely by pipeline pressure and closes slowly, so it suits large storage where a sudden shut-off would hammer the network.

Remote float (100X): the 100X-16P remote control float valve does the same job in cast stainless steel (CF8), covering DN40-DN300 at 0-1.0 MPa with a working temperature range of -50°C to 100°C — the specification for tanks holding corrosive or high-purity water, or for coastal plants where rust is the enemy.

For any of these valves serving a potable water network, place an HS41X anti-pollution backflow preventer at the connection point so tank contents can never flow backwards into the drinking water main — see our backflow prevention guide for the full cross-connection control picture.

5. Installation & Protection

Hydraulic control valves are only as reliable as their pilot system, and pilot ports are sensitive to particulates. Install a strainer at the valve inlet: the SGL41H telescopic Y-strainer is designed specifically to protect hydraulic water control valves and precision machinery, combining the strainer and an expansion joint in one body so the valve can be removed for service without cutting the pipeline. Filter screens are stainless steel 304/316, with 18-30 mesh for water duty.

Fit an isolation gate valve upstream and downstream of the control valve so the unit can be bypassed and maintained without draining the network. On pump-fed systems, protect the suction side as well: an EN12845 suction vortex preventer mounted at the pump suction eliminates vortexing and air entrainment, which prevents cavitation and the pressure spikes that damage both pumps and control valves.

Confirm orientation and space before ordering — flanged hydraulic control valves need straight access for the pilot tubing and room for the isolation valves. DN and end connection (ANSI/JIS/GB flange drilling) must be stated on the datasheet.

6. B2B Specification Checklist

• Define the controlled variable — downstream pressure (500X PRV), tank level (F745X / 100X), or electric on/off (GKZF-1 solenoid gate valve). A single line often needs two: a PRV feeding a level control valve at the tank.
• State size and pressure — DN20-DN600 for the 500X with nominal pressure 1.0/1.6/2.5 MPa; DN50-DN400 at 1.0/1.6 MPa for the F745X; DN40-DN300 at 0-1.0 MPa for the 100X-16P. Confirm inlet pressure and required set pressure (500X adjusts 0.1-1.6 MPa).
• Choose body material by media — ductile iron QT450-10 for clean water; cast stainless steel CF8 (100X-16P) for corrosive or hygiene-critical service.
• Nominate the connection standard — ANSI, JIS or GB flange drilling must match your pipeline; state it explicitly in the enquiry.
• Add protection accessories — SGL41H telescopic Y-strainer at the inlet, isolation gate valves, and an HS41X backflow preventer on potable connections; EN12845 suction vortex preventers on pump suctions.
• Verify the supplier first — pilot quality is invisible in photos. Require batch shell/seat test reports and material certificates, and run our B2B valve sourcing checklist before committing to a manufacturer.

Frequently Asked Questions