Description

Product Overview

A PP concentric reducer is an injection-moulded polypropylene fitting that connects two duct sections of different diameters. It is the fitting used where a PP duct run changes size – at equipment connections, where a main duct steps down to a branch, or where airflow is rebalanced along the run – and it matches the round PP duct range.

Concentric means both ends share the same centre line, so the transition is symmetrical around the duct axis. The reducer is injection moulded in PP or flame retardant PPs, in beige or grey, and joins the duct run by hot air welding, with socket connection reinforcement at the joints. For the straight duct the reducer connects to, see Polypropylene Round Ducts.

A duct reducer is one part of a ventilation system: it connects to straight duct, tees, elbows and other fittings rather than replacing them, and matching fittings are available from the same supplier so a complete PP duct line can be specified from one source.

Product Selection Summary

Good Fit

• PP duct runs that change diameter between two sections or at equipment connections
• Connecting equipment outlets or fan connections to the main duct size
• Corrosive exhaust and ventilation systems using the round PP duct range
• Projects needing flame retardant fittings for part or all of a run

Conditions To Confirm

• Inlet and outlet diameters (the two sizes being connected)
• Material grade: PP or flame retardant PPs
• Gas composition, concentration, temperature and moisture at the operating point
• Whether a standard size (φ20-500mm) covers the transition or a custom size is needed

Not a Replacement For

• Fans, airflow balancing devices, dampers or gas treatment equipment

Technical Specifications

Confirmed Product Parameters

Parameter	Value
Product Type	PP Concentric Reducer (polypropylene duct reducer)
Material	PP (polypropylene) or PPs flame retardant grade
Size Range	Standard sizes φ20-500mm; larger transitions (e.g. φ600mm) or custom per project
Connection	Hot air weld; socket connection reinforcement
Fabrication	Injection molding
Color	Beige / Grey
Working Temperature	-15℃ to 80℃
Chemical Resistance	pH 1-14 (acid and alkali)
Certification	ISO9001, ISO14001, RoHS

Standard sizes cover φ20mm to φ500mm. A transition to a larger diameter, such as φ600mm, or a non-standard pair of inlet and outlet sizes is made to order – confirm the two diameters against your duct schedule when inquiring.

Material & Performance

Because round fittings are injection moulded rather than welded from sheet, the reducer keeps the same corrosion resistance as the welded duct while offering consistent moulded dimensions, smooth internal surfaces and a shorter production time for standard sizes.

PP concentric reducers are injection moulded from polypropylene, chosen for corrosive fume handling in ductwork:

• Acid and alkali resistance: PP withstands corrosion by high-concentration acids and alkalis across a wide pH range (pH 1-14).
• Sound insulation: PP reduces vibration and noise caused by air flow through the size change.
• Light weight: moulded PP fittings are light and easy to handle and weld on site.
• Consistent moulded dimensions: each size is produced to a standard mould, giving uniform dimensions and wall thickness across batches.
• Long service life: PP duct systems offer a service life of up to 50 years under specified operating conditions.
• Anti-condensation: PP conducts heat poorly, reducing condensation and heat loss at the fitting.

Flame retardant PPs is available where fire-rated ductwork is required; specify the required flame retardant grade when inquiring. The material grade applies to the whole fitting, so a single grade can be specified across the duct, fittings and accessories in the run.

Applications

When a Duct Run Uses a Reducer

A reducer is used wherever the duct diameter changes along the run:

• Equipment connections – matching a fan, hood or scrubber outlet to the main duct size
• Main to branch steps – where a distribution main reduces before feeding smaller branch lines
• Flow adjustment – stepping the duct size to suit the airflow carried by each section
• Existing system modifications – joining new duct of a different size into an existing run

Because the concentric reducer keeps both ends on a common centre line, it is suited to vertical runs and installations where the duct axis must stay aligned through the size change. On horizontal runs the same fitting is used where alignment is not a constraint, and the welded transition keeps the whole section sealed as part of the continuous duct.

Selection Notes & Quotation Information

Inlet and Outlet Diameters

Confirm both diameters when ordering: the larger end and the smaller end of the transition. If one end falls outside the standard φ20-500mm range – for example a φ600mm connection – the reducer is made to order and the size pair is confirmed against your duct schedule and drawings.

To Quote PP Concentric Reducer

Provide: inlet diameter, outlet diameter, quantity, material grade (PP or flame retardant PPs), color (beige or grey), application, destination port, and your duct schedule or drawings.

MOQ and lead time are confirmed per project. Request a quote via WhatsApp or email using the contact block below.

Installation & System Integration

PP concentric reducers are joined to the duct run by hot air welding, and each joint is reinforced with a socket connection. The same joining method applies to straight duct, elbows and tees, so the reducer can be welded into the run as part of one continuous sealed system.

Where a run will be disassembled later for maintenance, flange connections are used at those points instead, so the reducer can be bolted between flanged sections.

Complete systems combine reducers with straight duct, tees, couplings and flanges. See the full range of PP duct systems.

Related Products

• Polypropylene Round Ducts
• PP Air Duct Tee
• PP 90° Elbow
• PP Air Duct Flange
• PP Air Duct Coupling
• Full PP Duct Range
• PP Air Duct Guide – a complete guide to PP duct types, sizes and materials.

FAQ

What is a PP concentric reducer?

It is an injection-moulded polypropylene fitting that connects two duct sections of different diameters, with both ends on a common centre line, used where a run changes size.

What sizes are available?

Standard sizes cover φ20mm to φ500mm. Larger transitions, such as φ600mm, or non-standard inlet-outlet pairs are made to order against your duct schedule and drawings.

Concentric or eccentric – what is the difference?

Concentric reducers keep both ends on the same centre line, suited to vertical runs and aligned connections. The XICHENG range offers concentric reducers as the standard fitting.

How is it connected?

By hot air welding to the duct run, with socket connection reinforcement at each joint – the same method used for straight duct and other round fittings.

Is flame retardant PP available?

Yes. The reducer is available in standard PP or flame retardant PPs; specify the required flame retardant grade when inquiring.

What do I need to provide for a quote?

Inlet diameter, outlet diameter, quantity, material grade, color, application, destination port, and your duct schedule or drawings.