Uni Bell

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Force Main Design Guide for PVC Pipe: Essential Insights

In the world of wastewater management, PVC pipes shine for force mains—pressurized lines carrying sewage when gravity won't cut it. This guide from the Uni-Bell PVC Pipe Association demystifies designing durable PVC force mains, emphasizing cyclic pressures from pump cycles. With over 40,000 miles in service since the 1970s, PVC resists corrosion, maintains smooth hydraulics (C=150), and lasts 100+ years.

Why PVC for Force Mains?

Corrosion-Free: Unaffected by hydrogen sulfide, unlike metals.

Efficient Hydraulics: Low friction reduces pumping costs; no degradation over time.

Proven Longevity: A 1989 installation met new pipe standards in 2009.

Cyclic Strength: Handles millions of pressure surges without failure.

Core Design Elements

Hydraulic design uses Darcy-Weisbach (roughness 7.0×10⁻⁶ ft) or Hazen-Williams equations. Key checks:

Working Pressure: ≤ Pressure Class (PC) × Thermal Factor (FT).

Recurring Surge: Normal pressure + surge ≤ PC × FT.

Occasional Surge: Max pressure + surge ≤ 1.6 × PC × FT.

Cyclic Life: ≥ Design life, using Folkman Equation for surge amplitude.

Surge pressures? Joukowsky Equation gives conservative estimates (e.g., DR 21: 16 psi/ft/s velocity change). Transient modeling offers accuracy for complex systems.

Design Example Walkthrough

For a 20-inch DR 32.5 pipe (PC 125):

Normal flow: 2,310 gpm, 76 psi.

Max flow: 5,070 gpm, 93 psi.

Surges: Recurring 29 psi (Joukowsky) or 50 psi amplitude (transient).

Cyclic life: 113 years (Joukowsky) vs. 211 years (transient) for 35,040 cycles/year.

Boost life by thicker walls, fewer cycles, or surge controls like VFD pumps.

Advanced Considerations

Entrapped Air: Use air valves per AWWA M51.

Multiple Surges: Miner's Rule combines events (e.g., start-ups add minimal fatigue).

Reflected Waves/Negatives: Model to avoid; PVC withstands negatives.

Installation: Follow guides for joint deflection and insertion.

Conservatism abounds: Joukowsky overestimates surges; Folkman Equation underpredicts failures. Apply FS=2 if needed.

Tools & Resources

Use PVCPA's Online Cyclic-Life Calculator for quick checks. For assessments, monitor pressures to estimate remaining life.

Share your force main stories in the comments! How has PVC performed in your projects? Tag @PVCPipeAssoc on X. For full guide, visit https://www.uni-bell.org/Blogs/Technical-Blog/Post/3662/PVC-Force-Main-Design-Guide

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External Load Design Calculator

A tool based on the Handbook of PVC Pipe Design and Construction to estimate external loads on PVC pipe. It uses conservative assumptions with safety factors, but designers remain responsible for proper application in their projects. 

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PVC Force Main Cyclic Life

PVC force mains have been used in North America since the 1970s, with over 40,000 miles in service. Research at Utah State University led to the Folkman Equation, a simplified method to analyze cyclic life—the pipe’s resistance to recurring surge pressures. This tool, featured in the Force Main Design Guide for PVC Pipe, allows engineers to:

Easily assess cyclic surges

Account for multiple pump/flow events

Estimate remaining cyclic life of in-service pipes

The method improves design accuracy while maintaining PVC’s inherent conservatism.

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UV Exposure/Sun Fading Has No Practical Effects On PVC Pipe Performance

As with many subjects, there is a germ of truth to the allegation: it is true that UV radiation from sunlight can affect the outermost surf

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Sample Specifications for PVC Water and Sewer Pipes

The Uni-Bell PVC Pipe Association offers sample specifications for water and sewer pipes.

The Uni-Bell PVC Pipe Association offers sample specifications for water and sewer pipes. Specifications are provided for three applications (water, sewer, and force main) as well as for PVCO pipe. There are also specifications covcering the requirements for sustainable piping products:

Potable water

Gravity sewer

Sewer force mains

PVCO pipe

Sustainable piping

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Evaluating Large Diameter PVC versus Fiberglass for sewer projects

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Large-Diameter Sewer Pipe: PVC vs. Fiberglass — What You Need to Know

Choosing the Right Pipe Material

Picking the right pipe material is a big deal — it directly impacts how cost-effective and reliable your sewer system will be for decades to come. For large-diameter gravity sewers, solid-wall PVC (polyvinyl chloride) and fiberglass (FRP) are two of the most commonly used options.

While some engineers still think of 18-inch pipes as “large-diameter,” ASTM standards have included sizes up to 36 inches since 1986 — nearly 40 years ago! For this comparison, we’re focusing on pipes ranging from 24 to 60 inches — sizes you’ll commonly find available in both PVC and FRP.

The Big Difference: Deflection

The main thing that sets these two materials apart is how they handle ring deflection when buried underground. Here’s the key point:

PVC pipe can handle significant deflection without any risk of material failure.

FRP pipe can only tolerate small amounts of deflection — push it too far and it can crack or fail.

So, if you’re designing with FRP, you’ll need to pay closer attention to controlling deflection. The flexible pipe design approach also shows that there’s no need to specify a stiffer PVC pipe just to match FRP — in fact, FRP usually needs higher stiffness than PVC to perform equally well in the ground.

Pipe Stiffness: Apples-to-Apples Comparison

Pipe stiffness is what keeps a flexible pipe from squishing under external loads. There’s a common myth that PVC needs extra stiffness to match FRP, but that’s not true. Both materials use the same ASTM D2412 test method to measure stiffness: Pipe Stiffness (PS) for PVC and Stiffness Number (SN) for FRP. They’re directly comparable.

Most PVC and FRP pipes are available with a stiffness rating of 46 psi, which is the standard for typical sewer jobs. For PVC, that’s usually plenty. For FRP, though, certain projects — like those with heavy loads or poor soil conditions — may require a stiffer pipe (like SN 90 or SN 120) to limit deflection within safe limits. PVC PS 46, on the other hand, handles almost all conditions with room to spare.

Installation: More Demands for FRP

In the field, the difference shows up in how you bury the pipe. PVC can handle deflection safely, so installation is straightforward. FRP, on the other hand, can fail if deflection goes beyond its limit — so contractors may need to tighten embedment requirements. That can mean using flowable fill, wider trenches, or simply paying more for higher-stiffness pipe.

The bottom line? To make FRP match PVC’s performance in the ground, you often need extra steps — tighter specs and more robust installation practices. PVC’s natural flexibility and resilience mean it rarely needs those added measures.

Key takeaway: Both PVC and FRP can be good options for large-diameter sewer lines — but PVC’s proven deflection tolerance and simpler installation can make it the more cost-effective and dependable choice for many projects.

To know more: https://www.uni-bell.org/Portals/0/ResourceFile/evaluating-large-diameter-pvc-versus-fiberglass-for-sewer-projects.pdf

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PVC & PVCO Hydraulic Calculator – Fast, Accurate, and Easy to Use

Need to calculate pressure losses in PVC or PVCO pressure pipe? Our Hydraulic Calculator does the heavy lifting using the Hazen-Williams formula – all in U.S. Customary units.

What It Does:

Quickly determines friction head loss based on your input:

Flow rate (gpm)

Pipe inside diameter (inches)

Pipe length (feet)

Hazen-Williams flow coefficient (C)

✅ Pro tip: Use C = 150 for PVC and PVCO — backed by lab and field testing. It's a conservative and reliable choice for your designs.

Optional: Add Minor Losses

Want even more precision? Just check the "Minor Losses" box and include losses due to:

Valves and fittings (using loss coefficients)

Equivalent lengths

Specified minor loss values

📊 Get Results You Can Use

Once you calculate total head loss, you can:

Add a static elevation value

Download a ready-to-use Excel spreadsheet

View a full head vs. flow rate chart across a range of conditions

📎 Why Trust the Numbers?

Years of testing show that PVC and PVCO maintain a high flow efficiency over time. That’s why we recommend C = 150 — it’s field-proven and design-safe.

👉 Click here to learn more Need accurate pipe flow data in seconds? Try our Hydraulic Calculator today.

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Hydraulic Testing of PVC Pipe Laboratory and Field Tests Confirm

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This calculator determines velocity, flow rate, or slope in PVC gravity sewer pipe using the Manning’s Equation (in U.S. Customary units):

Laboratory testing of new pipe and field testing of in-service pipe have both confirmed that a Manning’s “n” value of 0.009 is conservative for solid-wall PVC sewer pipe. This value is recommended for hydraulic design. Click here for more information.

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This calculator determines the friction head-loss in PVC and PVCO pipe using the Hazen-Williams formula (in U.S. Customary units):

Laboratory testing of new pipe and field testing of in-service pipe have both confirmed a Hazen-Williams flow coefficient of 150 is conservative for PVC and PVCO pipe. This value is recommended for hydraulic design. Click here for more information.

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Proven Performance of PVC Pipe in

The Uni-Bell PVC Pipe Association has completed a comprehensive two-part research initiative to evaluate the long-term performance of PVC sewer pipe in deep-bury conditions.

The first component used finite element analysis (FEA) to simulate how PVC pipe behaves under various soil and loading conditions. This modeling provided a detailed view of the expected structural response in deep installations.

The second component applied laser profiling technology to an in-service PVC sewer interceptor that has been operating for over 45 years, installed at depths reaching 28 feet. This method offered high-resolution data on the actual deflection and shape of the buried pipe.

FEA modeling answered the question, “What should it look like?” while laser profiling addressed “What does it look like?” The results from both analyses aligned closely, confirming that PVC pipe performs exceptionally well under deep-bury conditions with minimal deflection or structural degradation.

This dual-approach research provides strong evidence of PVC’s reliability and durability in demanding gravity sewer applications.

For detailed findings, read the full report: PVC Pipe in Deep-Bury Applications: FEA Modeling and Field Inspection of PVC Sewer Pipe.

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PVC and HDPE Pressure Pipes: Material Comparison

For municipal applications, PVC pressure pipe is manufactured and tested per the AWWA C900 standard and is available in sizes up to 60 inch

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The Uni-Bell PVC Pipe Association conducted a two-pronged research effort to evaluate the performance of PVC sewer pipes in deep-bury applications. The first part of the study used finite element analysis (FEA) to simulate how PVC pipes behave structurally under various loading conditions.

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Investigate performance of PVC sewer pipes in deep-bury applications.

Approach: Two-pronged research combining simulation and field data.

Finite Element Analysis (FEA): Modeled structural behavior of PVC pipes under different loads—provided a theoretical benchmark ("what should it look like?").

Laser Profiling: Collected real-world deflection data from a 45-year-old PVC sewer interceptor buried up to 28 feet deep—revealed actual performance ("what does it look like?").

The alignment of FEA predictions with long-term field data highlights the excellent structural performance and reliability of PVC pipe in deep-bury conditions.

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PVC Manholes in Gravity Sewer Systems

PVC Manholes in Gravity Sewer Systems

Manholes are vital for operating and maintaining gravity sewer systems. They provide essential access for inspection, cleaning, and repairs. Additionally, manholes control hydraulic flow at points of directional change, grade variation, or where flow channels merge. To prevent infiltration or exfiltration, manhole connections must be watertight.

Benefits of PVC Manholes

Watertightness: PVC manhole structures are made from pipe stock and joined via a thermoforming process, ensuring consistent, watertight seals throughout the body and at outlet stubs.

Corrosion Resistance: PVC is resistant to the harsh, corrosive conditions found in sanitary sewers, enhancing durability.

Lightweight: PVC manholes are significantly lighter than concrete alternatives, simplifying handling and installation.

Purpose and Capabilities

PVC manhole systems are designed to:

Meet structural requirements for traffic-bearing applications

Offer a watertight PVC structure and gasketed pipe connections

Accommodate pipe diameters up to 36 inches

Manufacturing Process

Manhole & Base Tee: These components are formed by thermoforming PVC pipe stock into the required shapes.

Pipe Connection Stubs: Also made from PVC pipe stock, these are shaped to form watertight connections with designated pipe systems.

PVC Manhole Structure

A standard PVC manhole consists of a circular PVC pipe section atop a precast concrete base. The upper portion may taper to a smaller diameter at the surface for space efficiency.

Specifications

Material: All components—manholes, base tees, reducing cones, and connection stubs—are made from PVC pipe stock that meets ASTM D1784, cell class 12454.

Joints and Gaskets: Gasketed joints comply with ASTM D3212, and gaskets meet ASTM F477 requirements for performance and watertight integrity.

Installation: Install using standard backfill materials and procedures for flexible pipes. Backfill should be granular and meet Class 1, 2, or 3 criteria as per ASTM D2321 and CSA B182.11.

To Know More: https://www.uni-bell.org/Portals/0/ResourceFile/pvc-sewer-manholes-and-drainage-structures.pdf