Types of Fittings for Gas and Water Pipes
Fitting Designs and Installation Considerations
When choosing the correct fittings, you need to know the difference between female fittings, which are threaded on the inside, and male fittings, which close around a female fitting. Pipes tend to end in male fittings, and there will be times when you will use a street fitting which has both a male and female end. You also need to understand the difference between supply fittings and DWV fittings.
Supply Fittings: Also known as pressure fittings, supply fittings rely on water pressure to maintain flow. They are used above ground to connect pipes that provide water to faucets and fixtures. There are a number of different designs available, each of which serves a special purpose.
- Designs: Tees are T-shaped fittings that divert water from one line to another. They have three identical female openings located at 90-degree angles from each other. Couplings are used to join the ends of two pipes in a straight line, while unions feature three separate pieces – a tail piece, thread piece and nut. With a union, you can connect or disconnect pipe in the middle of a line. They must be used when you are working with threaded pipe because you cannot screw pipe into both ends at once. Plugs are used to seal a fitting at the end of a pipeline to provide an easy setup for changes or additions that must be made to the line in the future.
- Features: Water supply fittings may be made of copper, PVC or CPVC. Crows feet tees connect a fourth pipe while elbow fittings, or ells, change the direction of a pipeline and feature two female threads. Elbows are most commonly curved at 45-degree or 90-degree angles. Street ells feature a female thread on one end and a male thread on the other. Use adapter couplings to connect a soldered or glued joint to a threaded joint. Caps are used to seal off the end of a pipe.
DWV Fittings: DWV stands for “drain-waste-vent.” These fittings use gravity to move used water and waste out of your house. DWV fittings alter the direction of waste flow gradually so it won’t get bogged down at any point. They are used with pipes that remove water from sinks, toilets and tubs. They also help in venting the drainage system by removing unwanted and noxious gases from your home. DWV fittings come in a wide range of designs.
- Designs: Elbow joints are available in a selection of angles ranging from 22.5 degrees to 90 degrees. Y-shaped fittings called “wyes” join two separate lines. A P-trap is attached beneath a sink, where it traps water in the arc of the fitting, sealing it in while preventing sewer gases from seeping into your house. Sanitary tees and long radius tees help with the removal of waste and water while vent tees have 90-degree angles for fittings used in the venting side of the system.
- Features: DWV fittings determine the slope of your piping system. As a general rule, slope pipe downward 1/4-inch for every horizontal foot of pipe. DWV fittings should be made from the same material as the pipes. Closet elbows connect a toilet to the main drain while wyes use a 45 degree angle to maintain an uninterrupted flow. Cleanouts offer a convenient way to unclog blockages in your drainage system.
Reduction and Transition Fittings: When two different sizes of pipe or pipe made from different materials need to be linked, special fittings are required. Reduction and transition fittings share similar designs. Reducer elbows, tees and wyes have one end that’s smaller than the other, allowing for the transition from one pipe size to another. They feature two female ends. Bushings function in the same way as reducers, but feature one male and one female end. Reducer couplings connect smaller diameter pipes with larger ones while transition couplings link copper or steel pipes to plastic ones. Some reducers reduce pipe more than one step in size. Dielectric unions are used when making the transition from steel to copper pipes.
How to measure the gas/water fittings you need
Gas fittings and hoses used in Australian Caravans and Motorhomes use a number of different threads. They may seem hard at first, but a short read will give you enough information to purchase the correct part.
The following information is educational and general in nature only. Licensed Gas Fitters are required to install gas fittings into RVs.
All gas components on this website that have threads also have a list of other components that will connect to them. They are listed below each product description. This feature allows you to ensure all components from gas cylinder to gas appliance are compatible.
1) BSP (British Standard Pipe)
BSP threads are the most common and can be used for gas and water. The sizes are imperial.
To get a 100% seal with gas you use a yellow thread or Liquid thread seal. You can use white or yellow for water.
When used for water the most common one you will know around the home is on your garden tap. Most garden hose fittings come with a 3/4" BSP to 1" BSP adapter.
The size quoted for threads is indicative of the internal bore size, not the diameter of the thread.
Click here to print a Thread Sight Guide to lay your thread on.
Above: If you have an existing thread that looks like those above, you need to measure the outside of the male thread as shown. The male thread is generally tapered so that it gets tighter when screwed in.
9.5mm measured OD is Male BSP 1/8"
13mm measured OD is Male BSP 1/4"
16mm measured OD is Male BSP 3/8"
21mm measured OD is Male BSP 1/2"
26mm measured OD is Male BSP 3/4"
33mm measured OD is Male BSP 1"
Above: If it is a female fitting, measure the inside to determine the actual name. Measured sizes are shown as approx. mm
8mm measured ID is Female BSP 1/8"
11mm measured ID is Female BSP 1/4"
14mm measured ID is Female BSP 3/8"
19mm measured ID is Female BSP 1/2"
24mm measured ID is Female BSP 3/4"
31mm measured ID is Female BSP 1"
2) SAE 45 degree flare
The male fittings are easily identified by the 45 degree flare at the end. These screw into either a SAE nut on the end of a copper pipe or a gas hose.
When used with copper pipe, the pipe is flared to 45 degree. The nut will not fall off and the copper section creates the seal between the nut and SAE 45 flare brass fitting. No thread tape is required with these fittings.
The Outside Diameter of the thread can be measured to give you the correct name of the fitting.
11mm measured OD is Male SAE 1/4"
13mm measured OD is Male SAE 5/16"
16mm measured OD is Male SAE 3/8"
Measure the Inside Diameter to get the correct name of the nut. The nuts always swivel. They have an inverted flare inside.
10mm measured ID is Female SAE 1/4"
11mm measured ID is Female SAE 5/16"
14mm measured ID is Female SAE 3/8"
The nut shown is a 5/16" nut because it fits on a 5/16" pipe.
The recommended pipe dia. for a typical gas installation within a Caravan or Motorhome is 5/16" copper pipe.
If you have a gas BBQ, Gas stove, Gas HWS, Gas heater and large Gas fridge - you may need 3/8" pipe, but your gas fitter can determine this.
3) POL fittings
Used on larger gas cylinders these have a Left Hand thread. Many male fittings have a rubber o-ring and must not be over tightened.
4) Primus gas cylinder threads
One notable difference with this thread is that gas will only flow after the fitting is fully inserted into the cylinder.
5) 3/8 inch Left Hand gas cylinder threads
Often called Companion but used by other brands as well.
6) Bayonet fittings
Used for removable gas appliances. The female fitting is used to supply the gas and comes in one size only. A rubber cap should be placed on these if subject to dust or dirt.
7) Inverted Flare 1/4
This is used at the end of gas pigtails that connect to a change-over value. The seal does NOT require thread tape.