Valves and Supports

Valves and Supports

Introduction

This chapter covers two categories of elements essential to mastering the plumbing trade: valves (control and isolation devices) and supports (anchoring and suspension systems for piping). For the Red Seal exam, you must not only know the types and their uses, but also the calculation rules, the requirements of the Canadian Plumbing Code, and the principles of hydraulic operation. An error in valve selection or support spacing calculation can lead to catastrophic failures, water hammer, or leaks under pressure.

Valves: Classification and Principles

Role and Terminology

A valve is a mechanical device that regulates, isolates, or controls the flow of a fluid in a piping system. Three main functions:

The pressure rating (PN) of a valve is expressed in kPa or psi (1 psi ≈ 6.895 kPa). The service temperature is also a selection criterion: brass valves are suitable up to approximately 90 °C, while ductile iron or stainless steel valves can withstand higher temperatures.

Isolation Valves

Gate Valve

The gate valve uses a gate (disc) that moves perpendicular to the axis of flow. It offers very low pressure drop when fully open, as the passage is straight. It is designed to be fully open or fully closed, never in an intermediate position (risk of disc erosion).

Butterfly Valve

The butterfly valve uses a rotating disc (butterfly) mounted on a shaft. It is compact, lightweight, and quick to operate (quarter-turn). It can be used for isolation and, to a lesser extent, for coarse regulation.

Ball Valve

The ball valve uses a perforated sphere (ball). A quarter turn (90°) is sufficient to go from the open to closed position. It offers excellent sealing and quick operation.

Needle Valve

The needle valve has a tapered needle that engages into a seat. It allows very fine flow regulation, but its pressure drop is high. It is used for instrumentation lines, air bleeds, and low flow rates.

Check Valves (Non-Return)

The check valve allows flow in one direction only. It protects against backflow and the return of contaminated water.

Important rule: a check valve must be installed with the flow direction arrow pointing in the direction of flow. An inverted installation completely blocks the passage.

Regulation and Safety Valves

Relief Valve

The relief valve is a protection device against overpressure. It opens automatically when pressure exceeds a preset threshold and closes when pressure drops back below that threshold.

Pressure Reducing Valve (PRV)

The pressure reducing valve maintains a constant downstream pressure despite variations in upstream pressure. It is essential in buildings where municipal supply pressure exceeds 550 kPa (80 psi), as excessive pressure damages fixtures and causes water hammer.

Backflow Preventer

The backflow prevention device prevents contaminated water from returning into the potable water supply. Common types:

Canadian Plumbing Code requirement: any backflow prevention device must be installed in accordance with CSA B64 and must be tested annually by a certified technician (for RPZ assemblies).

Pipe Supports

Role and Principles

Supports (hangers, clamps, guides, anchors) hold piping in place, control thermal expansion, prevent vibrations, and distribute loads. An inadequate support causes:

Types of Supports

Support Spacing

The maximum spacing between supports depends on the nominal diameter of the pipe, the material (copper, CPVC, PEX, steel), and the fluid being transported (water, steam, gas). The Canadian Plumbing Code (Article 2.6.3.1) requires that supports be spaced to prevent excessive stress.

Spacing Table for Copper Pipes (Water)

Spacing Table for CPVC and PEX Pipes

Note: plastic pipes expand more than copper; they require closer support spacing and guides at direction changes.

Calculating Load on Supports

The total load on a support is the sum of:

Formula: Total load (kg) = (pipe weight + fluid weight) × length between supports + accessory weight.

Example: A 1 in copper pipe (weight ≈ 0.68 kg/m) carrying water, with a spacing of 1.8 m:

This simple calculation allows you to verify that the chosen support (e.g., 1 in clamp, allowable load ≈ 45 kg) is more than sufficient.

Thermal Expansion and Compensation

Materials expand with heat. The coefficient of linear expansion (α) is crucial:

Formula: ΔL = α × L × ΔT, where ΔL is the change in length (m), L is the initial length (m), ΔT is the temperature change (°C).

Example: A 15 m CPVC pipe undergoes a temperature change of 40 °C.

ΔL = 61 × 10⁻⁶ × 15 × 40 = 0.0366 m = 36.6 mm.

This expansion must be absorbed by expansion joints (bellows, loops) or by expansion loops (direction changes). Anchors must be placed on either side of the expansion joint to direct the movement.

Canadian Plumbing Code Rules

The Canadian Plumbing Code (CPC) — published by the National Research Council of Canada — contains several articles relating to supports:

CSA B125.3 Standard: Performance requirements for copper and plastic pipe fittings and supports.

Water Heater Specific Valves

T&P Relief Valve (Temperature and Pressure)

The T&P relief valve is mandatory on every water heater. It must be:

Set pressure: typically 1034 kPa (150 psi) and a temperature of 99 °C (210 °F).

Emergency Shutoff Valve

A shutoff valve must be installed at the cold water inlet of the water heater, at a maximum distance of 1.5 m from the appliance, to allow its replacement without shutting off the building's water supply.

Common Pitfalls to Avoid

Summary

Exam Tips

This chapter gives you a solid foundation to tackle Red Seal questions on valves and supports. Review the tables, redo the calculations, and practice identifying valves in photos or diagrams. Good luck with your preparation!