Roof Tank House Pump Systems
Bulletin 259A

* Constant water pressure
* Emergency water reserve
* Fire standpipe reserve, if required
* Standard pumps, motors and controls
* Duplex and triplex units
* Automatic control of pumps
* Water level alarms

Type RT Systems are a popular solution to the problem of furnishing constant water pressure in a building. Float switches in the roof tank actuate the house pumps in the basement and the water in the tank provides a reserve for peak demand periods plus fire standpipe requirements.

The building is assured of constant water pressure regardless of demand rate or fluctuating supply pressure. The tank water capacity between pump cut-in and cut-out allows the pump to remain off except during periods of high demand.

RT Systems utilize standard Federal pumps, either close-coupled end suction (Bulletin 177) or horizontally split case double suction (Bulletin 185). The pumps can operate at 3450 RPM or 1750 RPM speeds.

A high-and-low water level alarm float switch plus indicating lights, bell and silencer are furnished with the system.

DUPLEX SYSTEM:
A duplex RT System includes two pumps, two on-off roof tank float switches to actuate the pumps, one high-and-low water roof tank float switch to actuate the alarm and one duplex control panel to include the following interwired internal components: (2) fused disconnect switches (or circuit breakers), (2) magnetic starters, (2) handoff-automatic switches, (1) automatic alternator to alternate the operating cycles of the pumps and provide simultaneous operation when required plus a high-and-low water alarm section.

TRIPLEX SYSTEM:
A triplex RT System includes three pumps, three on-off roof tank switches to actuate the pumps, one high-and-low water root tank float switch to actuate the alarm and one triplex control panel to include the following interwired internal components: (3) fused disconnect switches (or circuit breakers), (3) magnetic starters, (3) hand-off automatic switches, (1) manual transfer switch to permit changing of the pump operating sequence and provide simultaneous two-pump and three-pump operation when required plus a high-and-low water alarm section.

ACCESSORIES AND MODIFICATIONS
A rubber-in-shear vibration rail set should be installed under each pump. A Fed-flex stainless steel hose connection plus a pressure gauge should be installed on each pump suction and discharge connection.

Electrode controls in the roof tank are available in lieu of the standard float switches, if preferred.

Federal Type SP Water Pressure Systems (Bulletin 271) can be furnished for use in conjunction with Type RT Systems, if additional pressure boosting is required on the upper floors of a building.

FACTORY-ASSEMBLED SYSTEMS 
a Type RT Systems can be furnished factory-assembled and pre-wired if jobsite assembly is not desired. Factory-assembled systems include a steel base, check valves, gate valves, pressure gauges and copper suction and discharge headers. The factory-assembled systems are available only with close-coupled pumps.

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Selection Table - Close-Coupled Pumps 3450 RPM

Sizing The Pumps And The Roof Tank

PUMP CAPACITY
Pump capacity can be determined from the total number of fixtures to be served. The GPM ratings shown in the table below apply to each pump of a duplex or triplex unit. If abnormal water-demand fixtures (such as swimming pools, laundries or process work) are present in the building, add extra capacity to the pumps.

PUMP HEAD (TDH)
The Total Dynamic Head of the pump includes the height from the pump to the top of the roof tank (static head), plus friction loss through the pump discharge pipe and fittings, minus the minimum available street pressure.

Example:

ROOF TANK SIZE
Total roof tank capacity should be thirty times the GPM rating of the pump, plus required fire standpipe reserve.

Example:

ROOF TANK FLOAT SWITCH NOTES
A.  The top stops on the lead-pump and lag-pump float switch rods are the pump-off stops. They are set below the overflow level (E), below the high water alarm level (K) and below the ball-cock (if any).
B.  Set stops on the rod above and below the float switch arm so that the arm can move freely between them.
C.  The bottom stops on the lead pump (C1) and lag-pump (C2) float switch rods are the pump-on stops. The lead-pump-on stop is set higher than the lag-pump-on stop. They are both set higher than the low water alarm level (J) and the top of the domestic water downfeed line (F).
D.  Fire reserve downfeed line.
E.  Tank overflow level.
F.  Domestic water downfeed line.
G.  Cotter pin is set in bottom of each float switch rod.
J.  Set low water alarm stop (J) lower than the pump-on stop levels (C1 & C2) and higher than the top of the domestic water downfeed line (F).
K. Set high water alarm stop (K) higher than the pump-off stops (A) and lower than the overflow level (E).
L.  Float arm weight.
M.  Hollow-tube floats.
N.  Tank overflow line.
O.  Tank hatch. Place all float switches close to the hatch so that the floats and stops in the tank can be easily reached from the ladder.
R. Tank ladder.