INTRODUCTION

In hillside communities hydrant pressures will change in relation to how far they are in elevation below the reservoirs that supply them. Hydrants at lower elevations will often have static pressures that exceed 120 psi while those in the upper portions of a distribution zone may have pressures below 50 psi. Higher pressure hydrants are sufficient to deliver required fire flows to the scene through direct hose lays. Low pressure hydrants, on the other hand, must have an engine at the hydrant to relay pump in order to achieve the capacity of the hydrant. When laying supply lines uphill, relay pumping may be required to just get water out the end of the hose lay.

SMALL DIAMETER SUPPLY LINES

2½" and 3" supply lines Apparatus equipped with 2½" and 3" supply lines can equip their hose loads with "4-way valves" in order to establish rapid initial water supply (laying from hydrant to fire) and enable a later arriving engine to relay pump without interrupting water flow. The 4-way valve is connected to the end of the hose load. The hydrant person attaches the 4-way valve to the hydrant while the engine lays line to the scene. When the hydrant is opened, water is supplied to the engine operating at the scene using hydrant pressure. If hydrant pressure is insufficient to provide adequate flow, a second engine can connect to the 4-way valve and increase pressure by relay pumping through the established hose lay to the engine at the scene. Blake 4-Way Valve The Blake 4-Way Valve is an older device with a fairly simple operating premise. It consists of a large ball valve which directs water in 90 degree bends to the outlets. During normal operation the hydrant water is directed to the left hand outlet (as oriented to the photo) and down the supply line. The relay pumper will connect an intake line to the right hand outlet and discharge to the inlet that is opposite from the hydrant. When the control handle is turned 90 degrees to the right, water is then directed through the right hand outlet to the relay pumper. The relay pumper then discharges into the inlet opposite the hydrant connection (bottom of the picture) to supply the hose lay. Thanks to Oakland Sta. 24 for letting us work with and photograph their Blake 4-way valve and 1870's "horse" hydrant.

Blake 4-Way Valve Close-up of the controls