Surge Tank

Theory of Operation

The surge tank is the initial capture point for all water returned from the pool. Water is returned from the drains (at the bottom of the diving well) and from the gutters (around the pool perimeter). Water from the surge tank flows into the strainer basket prior to entering the main pump, as shown in the process flow diagram.

The flow from the gutters is highly variable, determined by the amount of activity in the pool and the pool water level itself. When the pool is very active, waves roll into the gutter drains. A sudden surge in pool activity can cause a surge in gutter flow, hence the name for the tank.

When a high amount of gutter flow is present, the drain flow must be restricted. Otherwise, the surge tank level rises and the gutter drain rate slows. Eventually, the gutters may appear to overflow, as the rate at which the water flows into the surge tank is slower than the rate at which the water is flowing in. This poses two issues:

• The amount of gutter water processed is reduced. The gutters capture water that has the potential to be the dirtiest in the pool. Debris (such as leaves, pollen), algae spores, and oils (from the skin, sunscreen lotion) collect on the surface. The sun's UV rays break down disinfectant (chlorine) most at the surface. It is important that this water be collected with priority.
• The calming effect of the gutters is reduced, as waves are no longer absorbed. This is undesirable during competition, as can will affect swimmers' lap times.

A low amount of gutter flow can also pose an issue. This occurs when the pool water level is low and/or there is little activity in the pool. If the drain flow is not increased accordingly, the surge tank level can drop, as the rate at which the water is pumped out exceeds the rate at which water enters.

Troubleshooting

When the automation system is operating properly, the surge tank is mostly self-sufficient. However, the operator may still observe issues from time to time.

Low Water Level

When the surge tank is too low, this is typically due to one of more of the following reasons:

• The pool water level is too low (the modulating drain valve is not present). Fill the pool.
• The modulating drain valve is malfunctioning, if present. Service the valve and/or controls.
• The main pump flow rate is too high. Reduce the outlet flow rate as detailed here (only after ensuring that other conditions are not present).

When a drain return modulating valve is not present, it is important that the drain return is restricted (the valve is partially closed). Otherwise, flow from the drain will potentially prevent adequate flow from the gutter return. In an ideal case, the surge tank should always have a modulating valve on the drain return.

High Water Level

Typically, high water in the surge tank is not of concern (unless it has nearly reached or exceeded the overflow point, of course). High water is usually the result of:

• A nominal or slightly elevated pool water level in conjunction with a large amount of pool activity (spilling water into the gutters).
• Limited flow into the filter system due to a plugged strainer basket or blockage elsewhere.
• Excess water in the pool due to over-filling or a significant rain event (in this case, some water may be removed via backwash at the operator's discretion).

All three scenarios, of course, assume the main pump is operating. The surge tank will rise to a relatively high level shortly after the main pump is disabled (it will match the pool level).

Known Deficiencies

A combination of age and inadequate repairs in the past have led to a number of known deficiencies with the surge tank. These deficiencies have both functional and (to a much lesser extent) aesthetic implications.

Future Overhaul

To fully address the known deficiencies, an overhaul of the surge tank is planned as the budget permits.

Modulating Drain Valve

Motorized Actuator

A Bray 70-0201H motorized valve has been selected for the application. This is a Bray Series 70 Actuator, with a 2,000 in-lb turning capacity, configured for 120 VAC on/off operation. A heater and auxiliary contacts are included.

The part number breakdown is approximately as follows (some interpretation):

Part Number		Description	Comment
Series	70	Series 70 (On/Off)
Supply	(blank)	120 VAC
Torque	0201	2,000 lb-in torque
Heater	H	Heater is included

This particular model has:

• A single-phase reversible permanent split capacitor induction motor.
• 2 x SPDT 10 A auxiliary switches.
• 2 x 3/4" NPT conduit entries.
• A 5 W PTC style heater (to drive out condensation).
• 30 second stroke time (at 60 Hz).

Other notes:

• The motor has an internal thermal trip set at 135 °C.
• Terminals are sized for #22 AWG to #14 AWG.

Valve

The recommended valve is a Bray 300800-11010119. An exact breakdown of the part number cannot be located, but it appears that it means the following:

Part Number		Description	Comment
Series	30	Series 30 (wafer)
Size	0800	8 inch
Base Part	11010	TBD	Unable to locate specifics.
Material Code	119	Body: Cast Iron Disc: Nylon Coated Ductile Iron Stem: 416 Stainless Steel Seat: EDPM

• Bray Series 30 wafer butterfly
• 8-inch (200 mm)
• Cast iron body, 416 stainless steel stem

S70 NEMA 4X 2,000 lb-in 24 VAC/DC

4-20 mA Aux Switches Heater Battery Backup

$3084.40

Bray 70-0201SVH