Honeywell Pressure Reducing Valve - 1/2" F x 3/4" M (Dual Thread)

The Honeywell D04FM is a high-quality pressure reducing valve (PRV) designed to protect your plumbing system from excessive mains water pressure. By reducing and maintaining a constant outlet pressure, it prevents pressure-related damage to pipes, fittings and appliances while also reducing water consumption and minimising flow noise throughout your installation.

This valve is particularly recommended for use alongside whole house water filtration systems, where consistent, regulated water pressure is essential for optimal filter performance and longevity. Excessive or fluctuating mains pressure can reduce filter cartridge lifespan and put unnecessary strain on filtration housings and fittings — installing a PRV before your filtration system helps prevent these issues and ensures your system operates as intended.

Built with a dezincification-resistant brass body and fibre-reinforced EPDM diaphragm, the D04FM is engineered for long-term reliability in potable water systems. The outlet pressure is easily adjustable between 1.5 and 6 bar using the green adjustment knob — no special tools required.

A key advantage of the D04FM is its inlet pressure balancing design. Fluctuations in mains supply pressure won't affect your set outlet pressure, giving you consistent, stable water pressure throughout your property.

Suitable for both horizontal and vertical installation (spring bonnet facing upwards when vertical). Handles inlet pressures up to 16 bar and operating temperatures up to 40°C per DIN EN 1567, or up to 70°C at a maximum operating pressure of 10 bar.

Key Features:

• ½" BSP male inlet x ¾" BSP male outlet (external thread on both sides)
• Ideal companion for whole house water filtration systems
• Outlet pressure adjustable from 1.5 to 6 bar
• Maximum inlet pressure: 16 bar
• Inlet pressure balancing — stable outlet pressure regardless of supply fluctuations
• Dezincification-resistant brass housing
• WRAS approved and meets KTW/W270 and ACS potable water guidelines
• G¼" pressure gauge port (gauge sold separately)
• Compact design — just 84mm long
• Suitable for horizontal and vertical installation

Technical Specifications:

• Connection: ½" BSP male inlet, ¾" BSP male outlet
• Nominal size: DN15
• Inlet pressure: max. 16 bar
• Outlet pressure: 1.5–6 bar (adjustable)
• Minimum pressure drop: 1 bar
• Max operating temp: 40°C (70°C at max 10 bar)
• Dimensions: L 84mm x H 106mm
• Weight: 0.32 kg
• Medium: Potable water

Data Sheet Download

Follow the manufacturer’s installation guidance and check all connections before leaving the installation.

Order before our dispatch cut-off — 3pm Monday to Friday, or 12pm on Saturday — and your order is sent the same day; anything after that follows the next working day. We don’t dispatch on Sundays, and you’ll get a tracking link by email as soon as your order is on its way.

Choose your UK delivery option at checkout:

• Free Express Delivery — free on orders over £60 (2–3 working days).
• Standard Delivery — £3.99 (2–3 working days).
• Next Day Delivery — £6.99, arriving the next working day when you order before the cut-off.

We also ship internationally, with rates calculated at checkout.

Returns & refunds

Changed your mind? You have 30 days to return any unused filter in its original sealed packaging for a refund, or 90 days for exchanges. Start at our returns portal and either generate a prepaid Royal Mail label (£3.49, deducted from your refund) or use your own courier — exchanges are always free to return. We approve refunds within 24 hours of your return reaching us; your bank may then take 3–5 working days to show the funds.