Double and single stub end sets differ in their component quantities and connection arrangements. A double set contains two stub ends and two backing rings for a joint with a stub end on each side. A single set contains one stub end and one backing ring for connecting an HDPE pipe to the existing flange of a valve or other equipment. A complete set also includes a gasket, bolts and nuts.
What is a stub end backing ring?
In an HDPE piping system, a stub end backing ring works with a stub end, which is fused to the end of the pipe. The ring supports the back of the stub end shoulder, while a gasket and bolts are used to assemble the joint with the mating flange.
The backing ring material and flange standard should match the equipment in the system. One example is a black-painted steel JIS 10K backing ring for a 110 mm HDPE stub end.
S.K. Fitting Valve supplies backing rings in black-painted steel, hot-dip galvanized steel (HDG), and SUS304 or SUS316 stainless steel.
What are stub end sets used for?
Stub end sets connect HDPE pipes to other pipes or flanged equipment. They create a joint that can be dismantled for maintenance or equipment replacement. The main components are:
- Stub end: A fitting fused to the pipe.
- Backing ring: A ring fitted behind the stub end shoulder, with holes for the bolts.
- Gasket: The sealing component between the mating faces. S.K. Fitting Valve generally supplies NR rubber gaskets in its standard sets. EPDM or NBR can be specified to meet the project requirements.
- Bolts and nuts: Fasteners that hold the connection together. Available options include zinc-plated, hot-dip galvanized (HDG), and SUS304 stainless steel.
S.K. Fitting Valve supplies double sets, single sets and individual components, including stub ends, backing rings, gaskets, bolts and nuts. Materials can be specified to suit the project requirements.
How do double and single stub end sets differ?
| Item | Double stub end set | Single stub end set |
|---|---|---|
| Stub ends | 2 | 1 |
| Backing rings | 2 | 1 |
| Gaskets in a standard set | 1 per joint | 1 per joint |
| Bolts and nuts | According to the set size and standard | According to the set size and standard |
| Connection arrangement | A stub end on both sides of the joint | A stub end on the pipe side, connected to an equipment flange |
| Typical application | HDPE pipe to HDPE pipe | HDPE pipe to a valve, pump or water meter |
Once you know which set is required at each connection, count the number of sets by the connection points, rather than by the number of valves or pieces of equipment.
How many sets do you need? Count the connection points
Count the flanged connection points that need to be assembled. One piece of equipment can have more than one connection, so one valve does not always require just one single set.
The examples below assume that no stub ends or backing rings have already been installed at the pipe ends.
| Connection arrangement | Sets required |
|---|---|
| HDPE pipe to HDPE pipe at one connection point | 1 double set |
| One HDPE pipe end connected to one equipment flange | 1 single set |
| One flanged valve with HDPE pipe connected on both sides | 2 single sets |
Two single sets connect pipes to a valve between them, creating two connection points. One double set joins two pipes directly at a single connection point.
Both arrangements use a total of two stub ends and two backing rings. However, two single sets have two joints and use two gaskets, while one double set has one joint and uses one gasket.
A request for “two stub ends” may therefore be unclear: it could mean one double set or two single sets. Describe the connection arrangement as well as the component quantity.
Should you buy a complete set or individual components?
For a new installation with no components at the connection point, you can request a quotation for a complete set. If some components are already installed or available, check what is missing and request only the items you need.
| Situation | What to request |
|---|---|
| A new connection with no components available | A double or single set, with the required included items clearly listed |
| Stub ends and backing rings are already installed | Check whether only gaskets and fasteners are needed, or whether additional items are required |
| Only the backing ring needs replacement | An individual backing ring, with details of the stub end and mating flange |
| Some suitable components are already available | List the available and missing items so the supply matches the application |
The quotation should define what “complete set” includes: stub ends, backing rings, gaskets, bolts and nuts. An itemized list makes it easier to check that all required components will be supplied.
What information helps you order the right set?
Start by explaining what connects to what. Then specify the number of connection points and the details of the mating components. This helps the sales team identify whether you need double sets, single sets or individual items.
Provide the following information:
- Connection arrangement: HDPE pipe to HDPE pipe, or HDPE pipe to a valve, pump or water meter.
- Pipe and equipment sizes: State the HDPE pipe size in millimetres and provide the flange details of the mating equipment.
- Number of connection points: If the equipment connects on both sides, specify that sets are required for both sides.
- Supply scope: A complete set, or only stub ends, backing rings, gaskets or fasteners.
- Project requirements: The required backing ring material, gasket type and fasteners.
If the equipment flange details are unknown, send a drawing, model information or a photograph of the equipment markings. In some cases, additional dimensions may be needed before the product list can be confirmed.
Example quotation request
Please quote stub end sets for connecting [specify] mm HDPE pipe to both sides of [specify quantity] flanged valves. We require [specify total quantity] single sets, including stub ends, backing rings, gaskets, bolts and nuts. The valve flange details are attached for checking the required items.
This request describes both the connection arrangement and the supply scope without requiring the buyer to begin with a full list of technical terms.
Frequently asked questions about double and single stub end sets
They may contain the same number of stub ends and backing rings, but they serve different numbers of connection points. Two single sets serve two connections, while one double set serves one connection. Check the gaskets, bolts and nuts against the actual connection arrangement.
No, provided the existing components remain suitable for the application. You can request only the missing items. Send the details of the existing components and the equipment to be connected so the required items can be checked before ordering.
Send a photograph or drawing showing the pipe ends and the equipment to be connected, together with the pipe size and number of connection points. This helps the sales team identify whether double sets, single sets or individual components are required.
It is a starting point, but it does not provide enough information to assemble the set. Also specify the pipe size, connection arrangement, number of connection points and flange details of the mating equipment.
Ask S.K. Fitting Valve about stub end sets
S.K. Fitting Valve supplies double and single stub end sets, as well as individual stub ends, backing rings, gaskets and fasteners, with material options to suit the project requirements.
Send your product list, drawing or connection photographs to request a quotation through LINE @skfitting, call 02-896-7744, or use the quotation request form
