Flexible Tap Connectors and Isolating Valves — Braided Hose Sizing, Under-Sink Installation, and Service Valve Types for UK Plumbers

Flexible tap connectors and isolating valves are among the most frequently fitted plumbing components on domestic jobs — every kitchen mixer, basin tap, toilet cistern, and washing machine connection requires them. Choosing the correct braided hose length, end connection size, and isolating valve type ensures a leak-free installation that meets Water Regulations and can be isolated for maintenance without draining the system.

This guide covers braided flexible hose sizing and end fittings, 15mm and 22mm tap connector options, straight and angled isolating valves, and how to select the right combination for kitchen sinks, basin taps, WC cisterns, and appliance connections.

Why Flexible Tap Connectors Are Used

Copper pipework in walls and under cabinets rarely aligns perfectly with tap tails — there is almost always a small offset between the supply pipe position and the tap connection point. Flexible braided hose absorbs this offset without the need for additional bends or extended copper runs, and it vibration-isolates taps and appliances from the copper supply so that thermal movement does not stress fittings over time.

UK Water Regulations (Schedule 2, Regulation 3) require that every tap and appliance connection is capable of being isolated without draining the whole system. A 15mm isolating valve installed on each supply before the flexible hose satisfies this requirement, and allows future maintenance — washer replacement, mixer cartridge swap, or appliance exchange — without shutting off water to the whole property.

Flexible Tap Connector End Fittings Explained

A flexible braided hose for tap connections has two ends: the supply end (connecting to the copper pipe or isolating valve) and the tap end (connecting to the tap tail). UK taps use BSP (British Standard Pipe) parallel thread on the tail — almost universally 1/2" BSP for kitchen and basin mixers, pillar taps, and toilet cisterns, and 3/4" BSP for bath taps and some commercial mixers.

Supply end options:

• 15mm compression — the most common supply connection, fits directly onto a 15mm copper pipe or 15mm isolating valve outlet. The standard for domestic kitchen and basin connections.
• 22mm compression — used where the supply pipe is 22mm, typically for high-flow taps, bath taps supplied from a 22mm branch, or in commercial settings.
• 1/2" BSP male — used when screwing directly onto a 1/2" BSP valve outlet rather than a compression fitting.

Tap end options:

• 3/4" BSP male — the standard for most UK kitchen mixers, basin pillar taps, and monobloc basin mixers. Screws into the tap tail nut.
• 1/2" BSP male — used with older taps and some specialist fittings.
• M10 or M12 metric thread — used with monobloc basin mixer taps that have slimline tails; check the tap manufacturer's specification before ordering.

Flexible Hose Lengths — Which to Choose

Braided hose for tap connections is available in standard lengths from 150mm to 500mm. Selecting the correct length avoids kinking the hose to make it fit (which stresses the stainless braid) or having excess hose that cannot be routed tidily under the sink.

• 150mm — used where the isolating valve is positioned close to the tap tail, typically under a standard vanity basin or kitchen sink where the pipe comes through the cabinet floor directly below the tap. This is the most compact option and looks neat in tight under-sink spaces.
• 300mm — the most commonly used length for kitchen sinks and basin units where the supply enters from the back wall or at a slight offset from the tap. Provides enough flexibility to allow the tap to be tightened from above without the hose pulling tight.
• 500mm — used where the supply pipe enters from a distance, for deep kitchen units, or when the isolating valve is mounted lower on the pipe run. Also used for washing machine connections where the inlet valve is further from the machine.

Product Cards — Flexible Tap Connectors

Both connectors feature 304 stainless steel braided outer sheath with EPDM inner hose and WRAS-compliant fittings. The stainless braid resists mechanical damage under the sink and meets the requirements of BS 6920 for water-contact materials.

Isolating Valves — Straight vs Angled

Every flexible tap connector installation requires an isolating valve on each supply pipe. UK Water Regulations (Schedule 2, Paragraph 15) require that fittings connected to the supply can be isolated without disturbing the rest of the system. A 1/4-turn screwdriver-operated isolating valve satisfies this requirement and allows the tap to be maintained or replaced in under five minutes.

Straight isolating valve: used where the supply pipe comes from directly below (floor entry) and the flexible hose runs vertically upward to the tap tail. The straight body gives a compact inline connection and minimal visual profile inside a cabinet.

Angled isolating valve: used where the supply pipe comes from the back wall (horizontal) or at an angle, and the hose needs to transition to a vertical connection to the tap. The 90° body replaces a compression elbow and isolating valve with a single fitting, reducing the number of joints under the sink.

Product Cards — Isolating Valves

Both isolating valves use a 1/4-turn flat-head screwdriver slot — slotted open when the slot is inline with the pipe, closed when perpendicular. Chrome-plated brass body suits under-sink and open-pipe installations where the valve may be visible. WRAS-approved for use on potable water supplies.

How to Fit a Flexible Tap Connector and Isolating Valve

1. Turn off the water — close the stop tap or zone valve for the floor above the work area. Open the affected tap to drain the pipe run.
2. Cut the copper pipe — using a pipe slice or hacksaw, cut the 15mm copper pipe 50mm below the underside of the cabinet top to leave room for the isolating valve body and hose connection.
3. Fit the isolating valve — slide the compression nut and olive onto the pipe. Insert the valve body, tighten the nut hand-tight, then a further 1.25 turns with a spanner. Do not overtighten — an olive on 15mm copper needs only finger-tight plus 1–1.5 turns.
4. Connect the flexible hose to the valve — the 15mm compression female end of the hose screws onto the 15mm male outlet of the isolating valve. Hand-tighten, then a further 1/4 turn. A fibre washer is included in the fitting — do not add PTFE to the compression end.
5. Connect the flexible hose to the tap — the 3/4" BSP male end screws into the tap tail. Use the fibre washer provided and tighten fully — a 1/4 turn with a spanner after hand-tight is sufficient for the BSP threaded connection.
6. Turn on and check — restore the water supply and inspect both ends of the connector and the isolating valve olive under light. A correctly fitted olive on 15mm copper shows no drips after 30 seconds under full pressure.

Braided Hose WRAS and BS 6920 Compliance

WRAS (Water Regulations Advisory Scheme) approval confirms that a fitting is manufactured from materials that do not contaminate potable water. Under UK Water Regulations, all fittings permanently connected to the supply — including flexible hoses — should be WRAS-approved or, for mechanical fittings, comply with BS 6920. Embrass Peerless flexible tap connectors carry WRAS approval, making them suitable for installations subject to Building Regulations Part G and local water authority inspection.

Common Applications by Room

Kitchen Sink Mixer

A standard UK kitchen mixer has two 3/4" BSP tails on 15mm copper supply pipes. Fit one straight 15mm isolating valve on each supply and two 15mm x 3/4" flexible hoses at 150mm–300mm length. This allows the mixer to be replaced without draining the system or cutting pipe.

Bathroom Basin

Most monobloc basin mixers use M10 or M12 tap tails — check before ordering. Pillar taps use standard 1/2" BSP. Fit a 15mm angled isolating valve on each 15mm copper supply entering from the back wall, then a 15mm x 3/4" (or x 1/2") flexible hose at 300mm length.

Toilet Cistern

WC cistern fills are typically 15mm supply with 1/2" BSP inlet valve. A 150mm straight flexible hose or a 300mm hose with a 15mm straight isolating valve gives full isolation for fill valve replacement — a 15-minute job rather than a system drain. See Toilet Cistern Maintenance for fill valve replacement details.

Washing Machine and Dishwasher

Appliance inlet valves use 3/4" BSP hose end connectors on 15mm copper supply pipes. A 15mm straight isolating valve (or a tee washing machine valve where there is no existing isolating valve on the branch) allows the appliance to be disconnected for service. Most machine inlet hoses are 1.5–2.5m and include 3/4" BSP ends — the isolating valve terminates the copper and the machine's own inlet hose connects directly.

Frequently Asked Questions

What size flexible tap connector do I need for a kitchen mixer?

Most UK kitchen mixers use 3/4" BSP tap tails on 15mm copper supply pipes. You need a 15mm x 3/4" flexible hose — the 15mm compression end connects to the pipe or isolating valve, and the 3/4" BSP end connects to the tap tail. Length is usually 150mm or 300mm depending on how far the copper is from the tap connection point.

Can I use a flexible hose without an isolating valve?

Technically a flexible hose can be fitted directly to the copper supply pipe, but UK Water Regulations require that taps can be isolated without shutting off the whole system. Fitting a 15mm isolating valve before the hose satisfies this requirement and makes future maintenance much faster — an isolating valve is inexpensive and takes two minutes to fit.

Do flexible tap connectors need PTFE tape?

No. Flexible hoses have two types of connection: compression (supply end) and BSP male (tap end). Compression fittings use a copper or brass olive — no PTFE needed. The 3/4" BSP tap end uses a fibre washer supplied with the fitting — no PTFE needed here either. Adding PTFE to a compression olive or over a fibre washer can prevent proper sealing.

What is the difference between a straight and angled isolating valve?

A straight isolating valve is used where the supply pipe enters from directly below (vertical floor entry). An angled valve (90°) is used where the supply pipe enters from the back wall (horizontal entry) and the hose or tap needs to run vertically — the angled body turns the direction in a single fitting, removing the need for a compression elbow.

How long should a flexible tap connector last?

Quality braided flexible hoses with EPDM inner hose and stainless braid typically last 10–15 years in normal domestic use. Factors that shorten service life include being stored kinked under a sink, being installed under sustained UV light, or contact with cleaning chemicals. As a precaution, many installers replace flexible hoses when replacing a tap, as the cost is negligible compared to the cost of a leak from a failed hose.

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APM Electricals
24 Western Avenue, Acton, London W3 7TZ
Phone: 020 8702 8080
Web: www.apmi.uk
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