PP Size Head

Product Model	Injection Molded Variable Diameter Series
Category	PP Molded Products
Reference Price	Price on request

Hot Customizable for Working Conditions 11 Technical Parameters

Product Overview

PP reducer, also known as a variable diameter pipe or eccentric fitting, is a transitional fitting used in ventilation duct systems to connect two pipes of different diameters. When the duct transitions from a larger to a smaller diameter, or when the inlet/outlet diameter of equipment does not match the duct diameter, the reducer ensures a smooth transition, avoiding eddies and increased air resistance caused by abrupt changes in duct cross-section.

The PP reducers supplied by Xicheng Environmental Protection are produced through injection molding in one piece, featuring seamless construction, no splicing, uniform wall thickness, and smooth inner surface. Made of polypropylene, they are available in standard PP and flame-retardant PP materials, resistant to acid, alkali, and salt corrosion, lightweight, and can be connected to formed ducts via slip-fit or flange methods for quick installation.

Reducers are categorized into concentric and eccentric types based on their shape. Concentric reducers have their two ends' centers aligned on the same straight line, suitable for vertical ducts and horizontally aligned ducts requiring high centering. Eccentric reducers have their two ends' centers not on the same axis, used for leveling the top or bottom of horizontal ducts to prevent liquid or gas accumulation at the diameter change point.

Working Principle

The working principle of reducers is to change the duct's flow cross-section through a conical transition section. As airflow enters from the larger end and flows along the conical inner wall to the smaller end, it gradually accelerates or decelerates. The continuously varying cross-section avoids localized eddies and pressure loss caused by sudden contraction. Compared to directly joining two flanges of different diameters, formed reducers provide smoother transitions, resulting in lower system operating noise and energy consumption.

In terms of corrosion resistance, the injection-molded PP reducers feature uniform material composition with no welds as corrosion weak points. Corrosive gases passing along the smooth inner wall do not contact metal, preventing rust. For slip-fit connections, matching PP welding rods or flange gaskets are used for sealing, maintaining corrosion continuity at the joint, making them suitable for acidic/alkaline waste gas and corrosive exhaust environments.

Structural Composition

Formed reducers consist of three parts: a large-end receiving socket, a conical transition section, and a small-end receiving socket, all injection-molded. The inner diameters of the two receiving sockets match the outer diameters of corresponding duct specifications, with the duct inserted and welded or secured with fasteners during connection. The conical transition section has uniform wall thickness, with the transition angle designed to balance structural strength and airflow smoothness.

Eccentric reducers, based on the concentric structure, shift the conical section to one side, keeping one end's outer edge flush. When used for leveling the top of horizontal ducts, they prevent gas accumulation at the top. When leveling the bottom, they prevent liquid accumulation at the bottom. The product's two ends can be designed as slip-fit sockets, flange edges, or butt-weld connections to accommodate different pipe connection methods.

Specification Model Table

The table below shows the specification representation and selection key points for reducers, with specific diameter combinations available in matching duct series.

Type	Connection Method	Applicable Scenario
Concentric Reducer	Slip-fit / Flange	Vertical ducts, aligned ducts
Eccentric Reducer	Slip-fit / Flange	Horizontal duct leveling
Flame-retardant Reducer	Slip-fit / Flange	Indoor fire protection requirements

Product Features

PP formed reducers feature a simple and reliable structure, serving as the standard solution for duct diameter changes. With smooth inner surface transitions and low airflow resistance, both concentric and eccentric types meet different installation needs for horizontal and vertical ducts, with specifications flexibly combinable based on upstream/downstream diameters. Key features include:

Injection-molded in one piece, no welds, fully corrosion-resistant with no weak points
Conical smooth transition, low air resistance, reduced eddies and noise
Concentric and eccentric types, adaptable to different installation requirements
Smooth inner surface prevents dust adhesion, corrosion-resistant and rust-free
Lightweight, slip-fit connection for quick installation, low labor costs
Specifications match formed duct series for easy selection
Available in flame-retardant material to meet indoor fire protection requirements

Material	PP / PPs Polypropylene
Molding Process	Integral injection molding
Type	Concentric / Eccentric
Connection Method	`Spigot / Flange`
Corrosion resistance performance	Acid-alkali-resistant salt
Flame Retardant Options	PPs self-extinguishing
Inner wall features	Smooth transition
Accompanying Pipes	PP Formed Ductwork
Section Type	Primarily circular
Function	Conic Transition Connector Our conic transition connectors are designed to seamlessly connect pipes of different diameters, ensuring
Specifications Range	Various bore combinations

Application Industries

Adaptation of ductwork and equipment interfaces in electroplating workshop ventilation systems
Flow transition between fan inlets/exits and main pipelines in chemical enterprises
Adaptation connection of acid/alkali exhaust branch pipes merging into main pipelines in semiconductor factories
Size matching between ductwork and dampers in laboratory ventilation systems
Non-circular connection between inlet/outlet of spray towers and ductwork
Contraction and expansion of exhaust pipelines in metallurgical pickling lines
Splicing and transition of different specifications of ductwork in environmental treatment projects

Typical Installation Locations

Reducer/adapters are installed at nodes where pipe diameters change, commonly found at fan inlets/exits, equipment interfaces, and branch pipes merging into main pipelines. Fan inlets/exits typically have smaller diameters than main ducts, and after expansion via reducers/adapters, they connect to the main pipelines, reducing outlet velocity and resistance. When branch pipes merge into main pipelines, eccentric reducers/adapters are used for alignment, ensuring horizontal pipes are flush at the bottom or top.

In waste gas treatment processes, reducers/adapters are located in transition sections between collecting branch pipes and main pipelines, main pipelines and purification equipment, and purification equipment and fans. When selecting, ensure the diameters of both ends of the reducer/adapter match upstream and downstream pipelines. For horizontal pipes, eccentric reducers/adapters are preferred, while concentric reducers/adapters are used for vertical pipes. After installation, ensure proper sealing and fastening. Before installation, verify the diameters of both ends, concentric or eccentric design, and flange standards. For horizontal pipes, determine the eccentric direction based on exhaust or liquid discharge requirements to avoid forming air or liquid pockets. After aligning the contraction section with upstream and downstream pipelines coaxially, tighten the connection. For spigot-and-socket connections, ensure the bonding surfaces are clean. Install independent support brackets near fans and pumps at contraction sections to prevent the weight and vibration of equipment from transferring to thin-walled sections.

For vertical pipes and applications requiring high alignment accuracy, concentric reducers are recommended. They feature coaxial ends, symmetrical diameter changes, and uniform stress distribution, making them easy to support and arrange. In horizontal pipes, eccentric reducers are chosen if the top or bottom of the pipe needs to remain level after diameter reduction (facilitating venting and preventing air pockets at the top, or draining liquid and avoiding liquid accumulation pits at the bottom). The flat side of the reducer should face the side requiring level alignment. For horizontal exhaust pipes containing liquid or dust, eccentric reducers with level bottoms are commonly used to maintain a continuous slope at the bottom, preventing liquid or dust accumulation at the reduction point. Clean gas pipes without liquid can also be selected with level tops for easy installation along beam bottoms. The choice between concentric and eccentric reducers should be determined based on whether the medium contains liquid or dust, the pipe slope, and installation space. Before installation, verify the flow direction and the orientation of the flat side.

Miter joints are typically made with socket connections. After inserting the duct into the socket, use weld electrodes of the same material to perform circumferential sealing along the joint. Alternatively, add bolts at the socket and pair them with sealant for fastening. This method offers quick installation and excellent sealing, making it suitable for fixed pipe sections. For locations requiring frequent disassembly for maintenance or connections to equipment,Flange connection (flange connection) is recommended. Both ends of the miter joint are equipped with flange edges, which connect to the duct or equipment flanges using bolts and gaskets for easy assembly and disassembly. Socket welding is cost-effective and airtight, while Flange connection provides flexibility and facilitates replacement. Choose the appropriate method based on the specific application. Regardless of the connection method used, inspect the joint for tightness and proper alignment after installation to prevent corrosive gas leakage. Negative-pressure pipe sections, in particular, must ensure continuous welds and intact gaskets. Post-installation, integrate system air leakage testing to verify the integrity of the connections.

Standard injection molded reducer covers common size combinations, with fast delivery and smooth inner wall; for special sizes, irregular interfaces, or non-standard equipment, PP sheet can be rolled and welded to produce reducers, which involves cone unfolding, cutting, rolling, and welding. Machined reducers offer high flexibility, capable of producing any size, length, and eccentricity, making them ideal for non-standard projects and on-site modifications. However, they have slightly lower appearance consistency and inner wall smoothness compared to injection molded parts, with a longer production cycle. Standard specifications are preferred for molded parts due to stable quality and fast delivery, while urgent, non-standard, and irregular transition parts should be considered for sheet processing. When custom machining, provide the port sizes, length, concentric or eccentric requirements, and connection method for one-time formation.

Nipples inherently create certain local resistance, but smoothly transitioned formed nipples have a very low resistance coefficient, with limited impact on the system's total airflow. What truly affects airflow are eddies caused by sudden diameter reduction or expansion, as well as additional resistance resulting from excessively high velocity selection and excessively short length after diameter change. During design, it is essential to control the airflow velocity of the pipes before and after diameter change within a reasonable range. Appropriately expanding the outlet of the fan and reducing the velocity can minimize dynamic pressure loss and regenerative noise. Using nipples reasonably and smoothly not only avoids significant airflow loss but also enhances the matching between the fan and the pipeline network, ensuring stable operation. What must be avoided is directly connecting two pipes with significantly different diameters using short nipples. When necessary, extend the transition section or implement segmented diameter change.

The PP formed size head is primarily used for ventilation and exhaust systems. Such pipelines typically operate at low pressure, where socket welding or flange connections can meet the requirements for sealing and strength. If used for liquid pipelines under certain pressure or positive pressure ventilation systems, it is necessary to verify the pressure rating, wall thickness, connection method, and sealing type of the pipe fittings. In such cases, thickened parts may be selected or full-welded reinforcement may be adopted. For liquid pressure pipelines, the weld strength and water hammer effects should also be checked, and selection should not be based directly on the standards for ventilation pipelines. When ordering, provide clear information on working pressure, temperature, medium, and connection dimensions, so that design personnel or manufacturers can select corresponding specifications based on the pressure rating. For applications involving pressure pipelines and safety requirements, it is recommended that professionals perform calculations before determining the model and wall thickness.

There are directional requirements. Although concentric reducers have symmetrical shapes at both ends, it is necessary to distinguish the large end and small end: the large end should connect to the incoming flow direction when reducing diameter, and the small end should connect to the incoming flow direction when expanding diameter. If installed in reverse, although it will not cause damage, it will affect the transition and flow direction. For eccentric reducers, in addition to the large end and small end direction, attention should also be paid to the eccentric direction. Top flat and bottom flat cannot be installed in reverse, otherwise, liquid accumulation, gas trapping, or poor drainage will occur in horizontal pipelines. For flanged reducers, it is necessary to verify the flange standards and hole position directions at both ends. Before installation, confirm the flow direction, concentric or eccentric type, and top/bottom leveling requirements according to the drawings, and mark the components before positioning. If there is doubt about the direction, verify it before welding to avoid rework after welding.

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