Reference Guide

THERMAL EXPANSIONAND CROSS-CONNECTIONCONTROL SOLUTIONS

As Seen On

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In a 40-gallon water heater,for example, water beingheated to recover afterusage will expand to about40.60 gallons when thedesired temperature isreached.

It expands! Reactingto physical law, waterexpands in volume asits temperature rises.

In the "Good Old" days

Before the advent of cross-connection control,expanded water thatexceeded the capacity ofthe water heater flowedback to the city main,where it easily dissipated.It was "open" at the citysupply side of the system,even though it was"closed" on the systemside.

Cross connectionmeans "no return"

Today, with back flow preventers, water meterswith check valves, and/orpressure-reducing valveswithout a bypass beinginstalled, expanded waterfrom a water heater cannot return to the citysupply. It is now a closedsystem, and expandedwater has no place to go.

COLDWATERSUPPLY

OPEN SYSTEM

When water is heated...

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Water is not compressible

Since water completelyfills the water heater and system piping beforerecovery starts, and sinceit can't be compressed,the expanded volume,even though small, has noplace to go.

As a result, the expandingwater creates a rapid and dangerous pressureincrease in the waterheater and system piping,much like the action of ahydraulic ram.

So "pop" goes the relief valve

The setting on a temper-ature & pressure safetyrelief is quickly reached,and the relief valveopens, losing heaterwater down the drain or,more often than not, allover the floor.

The illogical practice of operating your safety valveonce or twice a day is not only wasteful (you paid toheat the water that went down the drain), it's alsodangerous.

First of all, the T & Prelief valve youinstalled serves as an emergency con-trol only. It was neverdesigned as anoperating control.Once a safety valveis used on a dailybasis, it isn't thatsafe.

Deposits on the seat... deteriorating springs... wear-and-tear erosion can wear out a relief valve in no timeat all.

Dangerouspressuresbefore relief

What mostpeople don'trealize is thatd a n g e ro u sconditions can exist during thermal expansion longbefore the relief valve operates.

Internal pressures repeatedly occurring during recoveryperiods can collapse the center flue of a gas-fired waterheater, creating a hazardous presence of deadly carbonmonoxide gas, or even a water-heater explosion.

DANGER! BACK FLOW PREVENTERBFP

LOSTBTUs

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Even though the relief valve operates during eachrecovery period, high internal pressures occurring overand over again can accelerate tank leakage and short-en water-heater life, no matter how it is fired.

Controlled Pressure Rise During Thermal Expansion

The best solution to thermal expansion is to controlthe pressure it generates within a safe operatingrange, well below the emergency setting of a reliefvalve. This allows thermal expansion to occur withoutcausing a dangerous increase in pressure.

150 PSIG

SAFERANGE

Solution

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AIRCUSHION

AIRCUSHION

AIRCUSHION

EXPANDED WATER

This is easily accom-plished by adding anexpansion tank with asealed-in, compressibleair cushion, which willcompress as thermalexpansion occurs, pro-viding the place for theexpanded volume ofwater to go duringrecovery.

By sizing the air cushionaccording to Boyle'sLaw, we can select the maximum pressureon the system whenthe total amount ofexpanded water hasbeen generated.

When hot water is usedin the system, the pres-surized air cushionforces hot water backinto the system for use,not waste.

The thermal expansion tank features the sealed-in aircushion, pre-charged to the minimum system pres-sure before recovery is started. A rugged butyldiaphragm seals in the air cushion and also separatesair from hot domestic water to prevent air from beingdissolved by hot system water.

Finally, on the water side of the expansion tank is aseparate, rigid polypropylene liner so fresh, corrosive,domestic hot water can be handled without fear of corrosion and leaks.

1. SystemConnection

2. Separate, rigidpolypropylene-lined waterreservoir (NSFlisted)

3. Heavy-dutybutyl diaphragm

4. Sealed-in, permanent aircharge

5. Welded steelpressure sup-port domes

6. Air chargingvalve

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Sizing charts based on:

• Precharge matched to incoming supply pressure prior to installation

• Incoming water temperature 40°F

• 150psi T & P safety relief valve

AMTROL’s Therm-X-Trol® brochure MC#4090contains precise sizing guidelines for sytems notcovered in the above charts.

The thermal-expansion tank for domestic waterheaters, sized right, is the only logical answer to thegrowing problem of thermal expansion in waterheaters protected by BFP, check valves or pressure-reducing valves. A simple installation to the supplyside on the water heater, this small tank will eliminatethe dangerous condition so that the relief valve will notopen during normal heating cycles.

BACK FLOW PREVENTERBFP

Water Heater* Size (gals.)

Static Supply Pressure (psi)**

40 ST-5 ST-5 ST-5

50 ST-5 ST-5 ST-5

60 ST-5 ST-5 ST-8

80 ST-8 ST-8 ST-12

120 ST-12 ST-12 ST-25V

40 60 80

Max. Temp. Setting 140°F

Water Heater* Size (gals.)

Static Supply Pressure (psi)**

40 ST-5 ST-5 ST-5

50 ST-5 ST-5 ST-8

60 ST-8 ST-8 ST-8

80 ST-8 ST-8 ST-12

120 ST-12 ST-12 ST-25V

40 60 80

Max. Temp. Setting 150°F

Water Heater* Size (gals.)

Static Supply Pressure (psi)**

40 ST-8 ST-8 ST-8

50 ST-8 ST-8 ST-12

60 ST-8 ST-12 ST-25V

80 ST-12 ST-25V ST-25V

120 ST-25V ST-25V ST-25V

40 60 80

Max. Temp. Setting 180°F

MC# 8550 PN: 9015-612 (06/07)

®

Corporate Headquarters1400 Division Road West Warwick, RI 02893Telephone: 401-884-6300Fax: 401-884-5276

AMTROL Canada, Ltd.275 Shoemaker Street Kitchener, Ontario N2E 3B3Telephone: 519-478-1138Fax: 519-748-1138

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