Tank to Pump

Nozzles & Equipment

Siamese

A siamese is an appliance that combines two or more incoming lines into a single outgoing line — the mirror image of a wye. It is used to feed one demanding line or system from multiple supply hoses.

Schematic of a siamese appliance: two supply inlets on the left, Inlet A and Inlet B, each with a clapper plate, converge through a central combining casting into a single outlet pipe on the right. The outlet is labelled with its pressure and combined flow, and a readout shows the outlet pressure equals the supply minus the appliance loss regardless of how many lines feed, while the combined flow doubles with the second line.

Siamese connection · interactive

ONE LINE FEEDINGOne supply line is feeding the outlet. The clapper on the open, unconnected inlet stays seated — the water cannot back-feed out the unused side, so a single line is enough.

A clapper on the open, unconnected inlet is holding shut — no back-feed out the unused side.

Supply100 psi / line→ outlet90 psi·175 gpm

One line feeding: about 90 psi at the outlet. Add the second line and the pressure stays about the same — the flow doubles, the pressure does not.

A siamese adds flow, not pressure — the mirror of a wye, which divides flow, not pressure.

Inlets

The lesson is the clapper: connect just one inlet and the outlet still flows, while the other inlet's clapper holds shut so nothing escapes the unused side. A siamese is the mirror image of a wye — two lines in, one line out. This is a training aid; follow your SOPs and your apparatus's own appliances and limits.

Toggle each inlet and drag the supply pressure: two lines combine into one outlet, but the outlet pressure stays at the supply minus the appliance loss whether one or both feed — a siamese adds FLOW, not pressure. (Connect just one and the other inlet's clapper holds shut.)

Where a wye divides, a siamese merges. Combining two supply lines into one reduces the friction loss the supply sees, which is useful when a single large line cannot deliver the needed flow over distance.

A fire department connection on a standpipe or sprinkler system is essentially a siamese inlet, letting the engine pump into the building through more than one hose at once.

See also