Hi all experts and thanks in advance for your help!

I live in Alameda County in northern CA in a hillside house.
The pipe leading up to the street main sewer line is a 3" PVC, about 400 ft long, with an elevation difference of about 40 ft.

~2 Years ago, I had professional plumbers repair my sump pump float. They also replaced the last pipe section to the pump with a new check valve.
They used a rubber reduction coupling (shown in attached photo) to connect the 3" main pipe to the 2" pump pipe.

Last month, the coupling failed, shifted out of place, causing a spill of the entire pipe content into my back yard. you can do the math, it's ~150 gallons... at ~17.5 PSI...

My question is:
Is this coupling allowed by code to be used on pressurized lines?
I see it (or very similar item) on home depot web site, where it explicitly says this is for DWV: http://www.homedepot.com/p/3-in-x-2-in-PVC-DWV-Mechanical-Flexible-Coupling-P-32/

If the plumber did commit a code violation, where is the relevant code section, and what do you think is the extension of the plumber's liability for this spill?

Thank you for your thoughts!

Ami

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Most of the check valves for sump pumps have rubber couplings similar to that.
I've never had to install one with 40 feet of head, and 400 feet of distance. That's a lot of pressure on a fitting like that. I don't know if you can go back on the plumber for that, but for the repair I would consider a fitting made for pressure, a water supply fitting. That is more like a drainage fitting, which most of the time, has been working good enough. But 40' and 400'? Sounds like you need to up the game on that.

Hi Terry and thanks for your prompt reply.
I have already replaced the rubber coupling with a schedule 40, solid PVC one cemented in place...

My question is really about the code; is using this rubber coupling in a pressurized line a violation of plumbing code or not?
I would like to clearly establish liability here as the plumber refuses to accept any of it.

Thanks,

Ami I think you are saying that you have a sealed septic pit pumping household sewage uphill under pressure.

I have already replaced the rubber coupling with a schedule 40, solid PVC one cemented in place...

I can't help on the code. I will point out that with 400 ft, there is a lot of expansion and contraction with temperature. http://www.charlottepipe.com/Documents/PL_Tech_Man/ExpansionandContraction.pdf has the gory details. Page 57 and 57 describe the use of a "loop" to allow contraction and expansion. If you still have access, you might want to convert your repair.

Because your pipe has mostly been buried for a while, you will see less temperature change than you would right after installation. But still there are temperature changes including changes due to the contents.

Also, is that solid PVC pipe, which is pressure rated? Foam core pipe looks the same and is the same size. So while things are uncovered, you might read the markings if you want to know. Since it is California, and they usually use ABS for foam core pipe there, it might make it more likely that you have pressure rated PVC. Around here, most 3 inch PVC pipe would be the non-pressure type, and you have to check the markings if you want it for pressure.

I think you are saying that you have a sealed septic pit pumping household sewage uphill under pressure.


I can't help on the code. I will point out that with 400 ft, there is a lot of expansion and contraction with temperature. http://www.charlottepipe.com/Documents/PL_Tech_Man/ExpansionandContraction.pdf has the gory details. Page 57 and 57 describe the use of a "loop" to allow contraction and expansion. If you still have access, you might want to convert your repair.

Because your pipe has mostly been buried for a while, you will see less temperature change than you would right after installation. But still there are temperature changes including changes due to the contents.

Also, is that solid PVC pipe, which is pressure rated? Foam core pipe looks the same and is the same size. So while things are uncovered, you might read the markings if you want to know. Since it is California, and they usually use ABS for foam core pipe there, it might make it more likely that you have pressure rated PVC. Around here, most 3 inch PVC pipe would be the non-pressure type, and you have to check the markings if you want it for pressure.

Hi Reach and thanks for the detailed reply.
You are correct that the pipe is sealed and constantly under pressure.
The tank itself is not sealed. The pump has a float switch, and the check valve keeps the pressure in the pipe when the pump is off.

There is room for the pipe to move slightly. I have 2 more 2" heavy duty rubber couplings, and the end also has some room to move as the pump is 'hanging' from it in the tank. I'm attaching a photo of the whole setup with the new piping.
I am in north CA, so extreme weather is not an issue.
The pipe is Schedule 40 PVC. It is from the late 80's when the house was built.

Thanks again for your detailed reply.

I hope someone can help me with the code question.

Thanks,

Ami

P.S. See attached photo of setup with new piping

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• IMG_.JPG

Rigid vs Flexible Couplings for Industrial Applications

Industrial applications regularly use rigid and flexible couplings to connect shafts. These couplings transfer torque from one shaft to another. Rigid shafts transfer more torque but require no misalignment between the shafts. Flexible couplings allow for some misalignment, typically up to 5° in parallel, axial, or angular directions. This article provides an overview of rigid and flexible couplings and offers example applications for each type.

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Types of rigid and flexible couplings

There are various types of rigid and flexible couplings within industrial applications. It is important to first understand the application requirements to then know what parameters to look for in a coupling. The overview below is not a complete list, but gives an overview of the common types.

Rigid couplings

Rigid couplings connect shafts that are perfectly aligned. These couplings cannot compensate for misalignment during operation but can transfer higher torques. They are simple and cost-effective couplings and come in a variety of styles that make them application specific:

• Flanged couplings: Flanged couplings consist of two separate flange ends that bolt together. These couplings can handle heavy loads and have diameters larger than 200 mm (8 in). Flanged couplings can connect shafts of different diameters.
• Ribbed couplings: Also called clamp couplings, ribbed couplings connect shafts of the same diameter. These couplings are split through the center along their length. The two coupling pieces fit over the ends of two shafts to join them together. Then the coupling's two pieces are joined with bolts. These couplings are easy to install and are suitable for medium to high speeds.
• Sleeve couplings: Sleeve couplings are simple to use and install. The shaft ends insert into opposing ends of the sleeve, and set screws tighten the sleeve coupling to the shafts. These couplings are suitable for light to medium-duty applications.

Flexible couplings

Flexible couplings operate similarly to rigid couplings, transmitting torque from one shaft to another so both shafts move in unison. The primary difference is that flexible couplings allow for some misalignment between the two shafts in an angular, parallel, or axial direction. Some couplings allow for misalignment in a combination of directions.

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• Set screw couplings: A set screw coupling (Figure 1) connects two shafts together at their ends for the purpose of transmitting power. It contains one or more set screws that tighten against the shafts to secure them in place and prevent slippage. The spiral cuts around the coupling's body allow for slight flexibility.
• Gear couplings: Gear couplings transmit the most torque of any flexible coupling. These couplings consist of two hubs with external gear teeth that are an external/internal pair. The flanks of the gear teeth are designed to allow for up to 4° to 5° of misalignment.
• Jaw couplings: Jaw couplings are often used in continuously running electric motors. They handle angular misalignment up to 1 degree and parallel misalignment up to 0.015 inches. Jaw couplings are popular for being reliable, protective, and versatile.
• Grid couplings: Grid couplings are notable for reducing up to 30% of vibrations and cushion shock in driving and driven power transmission equipment.
• Roller chain couplings: Roller chain couplings are a cost-effective choice for high torque applications found in industries such as agricultural and mining. They permit approximately 2° of misalignment.

Selecting couplings for industrial applications

The following is an overview of industrial applications that use rigid or flexible couplings.

Rigid coupling applications

• High-speed rotating machinery: Turbines, high-speed pumps, and compressors use rigid couplings. Precise alignment is necessary to prevent vibration which inhibits smooth operation.
• Precision CNC machining: CNC machines use rigid couplings for accuracy and minimal backlash, which are both necessary for cutting, milling, and turning operations.
• Robotics and automation: Automated machinery and robotic systems use rigid couplings for precise motion control and synchronization between multiple axes.
• Power transmission systems: Heavy-duty power transmission applications use rigid couplings for high torque and shaft alignment.

Flexible coupling applications

• Electric motor driven equipment: Electric motors have flexible couplings to connect to pumps, compressors, fans, and other driven equipment to reduce vibration transmissions.
• Automotive industry: Drivetrains and suspension systems use flexible couplings to minimize vibrations and handle any misalignment caused by engine movements.
• HVAC systems:HVAC systems use flexible couplings to connect motors to fans, blowers, and other equipment.
• Marine and offshore applications: Marine propulsion systems, offshore drilling rigs, and ship-to-shore equipment use flexible couplings to handle misalignments caused by vessel movements.

FAQs

Why are flexible couplings preferred over rigid couplings?

Flexible couplings are preferred over rigid couplings for applications where misalignment between the shafts can occur.

Why use rigid coupling?

Use rigid coupling for applications in which there is no misalignment.

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