Almost every stainless press job ends at a thread somewhere: a valve, a meter, a pump, a tap or a gauge. The Standard Press 316 stainless range has five ways of getting there, and picking the right one saves you joints, offcuts and the odd wrestle with a fitting that has to spin on the tube.
The five adaptors
| Adaptor | Ends | Size range | 22mm x 3/4" price |
|---|---|---|---|
| Male BSP | Press x male thread | 15mm x 1/2" to 108mm x 4" | $22.06 |
| Female BSP | Press x female thread | 15mm x 1/2" to 108mm x 4" | $21.56 |
| Male BSP, tube end | Spigot x male thread | 15mm x 1/2" to 54mm x 2" | $24.40 |
| Female BSP, tube end | Spigot x female thread | 15mm x 1/2" to 28mm x 1" | $22.04 |
| Female BSP swivel nut | Press x loose female nut | 15mm x 1/2" to 54mm x 2-1/2" | $19.47 |
Press-socket adaptors: the standard choice
The male and female BSP adaptors press onto the tube like any other fitting and give you a fixed thread. They're the widest-ranging (up to 108mm x 4") and come in plenty of step-up and step-down combinations, like 22mm x 1/2" or 35mm x 1", so you can often skip a separate reducing bush. Use them where the thread is screwed in before the pipework is fixed, or where the threaded item can turn onto the adaptor.
Tube-end adaptors: cut out a joint
A tube-end adaptor has a spigot instead of a press socket. The spigot pushes into the socket of another press fitting, such as a tee, bend or coupling, and is pressed there. That means no short length of tube and one fewer press joint.
The trade-off at 22mm x 3/4": the male tube-end adaptor is $24.40 against $22.06 for the standard male adaptor, but the standard one needs a tube offcut and an extra press. In tight manifolds and plant rooms, the tube-end version usually wins.
Swivel nut adaptor: for things that can't turn
The swivel nut adaptor has a loose female BSP nut, so you can make up to a meter, pump, strainer or flexible connector without rotating the fitting on the tube or the equipment on its mounts. The listing names meters, pumps, strainers and equipment as its job, and its sizes include ones you'll meet on meters and pump ports, such as 42mm x 1-3/4" and 54mm x 2-1/2". Loose-nut joints seal on a flat face with a washer, so make sure the right washer is in place for the service.
Threaded bends and wall plate bends
Where the thread comes off at 90°, a press bend with a BSP end saves a bend plus an adaptor: female BSP bends run 15mm x 1/2" to 35mm x 1-1/4", male BSP bends 15mm x 1/2" to 54mm x 2". At tap and hose cock points, the wall plate bends fix back to framing. See fixing stainless press pipework.
The range also lists metric-thread adaptors (M20 x 1.5 to M50 x 1.5) for equipment with metric ports, but they aren't available to order yet.
Sealing stainless threads
- Stainless threads can gall, where the surfaces seize as they're tightened. Use a thread sealant suited to stainless and to the service (approved for potable water on drinking-water lines), and don't over-tighten.
- Tighten the thread before you press where possible, so you're not twisting a finished press joint.
- Hold the fitting with a spanner on its flats, not by the tube, if you must tighten after pressing.
- Copper to stainless: a threaded joint is the place to change systems. Don't press one system's fitting onto the other's tube. See stainless press sizes explained.
If the equipment needs to come out later, a union beats a plain adaptor. See unions in stainless press.
Frequently Asked Questions
What is a tube-end press adaptor?
An adaptor with a spigot instead of a press socket. The spigot pushes into another press fitting's socket and is pressed there, saving a tube offcut and a press joint.
When should I use a swivel nut press adaptor?
When connecting to a meter, pump, strainer or other equipment that can't be rotated. The loose nut tightens onto the thread without turning the fitting or the equipment.
Do stainless threads need special sealant?
Use a sealant suited to stainless and approved for the service. Stainless threads can gall, so avoid over-tightening.
Can I connect stainless press to copper?
Yes, through a threaded joint. Don't press a stainless fitting onto copper tube or a copper fitting onto stainless tube.