Frozen water pipes have caused millions of dollars worth of damage to hundreds of thousands of homes. Now a unique plumbing valve system recently put on the market makes it possible for a homeowner to protect himself against this kind of damage, even if there is a sudden freeze when the house is not occupied, and even if it happens during a power failure.

Called the Freeze-Gard Drain Valve System, it consists of three special self-powered (by the water pressure already in the system) values that respond automatically when the temperature inside the house drops close to freezing.

When properly installed in an existing plumbing system, these valves will perform two functions simultaneously to protect pipes and other appliances against freezing: They will shut off the incoming water supply to the house (from the municipal water lines on the outside), and drain the entire plumbing system in that building.

This would include the water heater, the boiler, radiators and heating system lines (in houses that are heated by hot water or steam).

All this happens automatically when the thermostatic valve (one of the three valves supplied) senses an air temperature of 40 F or less.

Ideal for homeowners who often go on winter vacations and are reluctant to drain their plumbing systems or shut down their heating systems, Freeze-Gard valves can also provide protection against freeze damage in second homes that may be unoccupied for weeks at a time.

Even in a house that is normally occupied during the winter, installing one of these systems can provide permanent insurance against the damage that could be caused by freezing water pipes, damage that could run into thousands of dollars. This new valve system will prevent damage by draining the system before pipes get cold enough to freeze, yet it can be quickly and easily reset manually (and the water turned back on) when heat is restored or the temperature rises.

Manufactured and distributed by Sheltech, Inc., 49 Middlesex Rd., Darien, Conn. 06820, the Freeze-gard System is sold through several plumbing supply houses in New England.

It can also be ordered from the manufacturer in areas where it is not yet available through normal channels. It has been listed and/or approved by several state agencies in the Northeast (it is not actually forbidden by any state or local codes because it is the first of its kind and none have considered anything like it before).

The "brain" of the system is the thermostatic valve assembly, actually a fairly simple device that works like the thermostat in the home heating system. It is connected to a water line inside the house, in an area that is likely to get cold before the rest of the house does (it can be mounted directly on the water pipe, or connected to it by means of flexible plastic or metal tubing). When the air temperature around this valve drops to 40 F, a mechanism on the inside allows water from the line to which it is connected to flow through the valve and out into another length of tubing that connects this unit with the auxiliary valve assembly.

The auxiliary valve is located where it can drain the lowest pipe or appliance in the house, usually in the basement. It, too, is connected to the low point in the piping by flexible tubing. Normally, the drain port in the auxiliary valve is closed, but when water flows to it from the thermostatic valve (after that valve has been opened by a drop in temperature), the pressure change on the inside of the auxiliary valve mechanism causes a piston or spool to shift. This opens a port that allows water from the piping or appliance to drain out, while it simultaneously sends a stream of water to the main valve assembly through another piece of tubing.

The main valve assembly is installed in the incoming water line, close to the point where the pipe enters that normally allows water to flow through it to the household plumbing system. However, when the stream of water arrives from the auxiliary valve, a change in internal pressure causes the spool to shift and shut off the incoming water supply. Simultaneously, it drains the remaining water out of the lines connecting it with the other valves and the rest of the system.

The drain ports on the two valves come with threaded openings so that tubing can be attached to dispose of the water harmlessly. Usually this means routing it to a drain in the basement floor, or a sump pump. (If the sump pump depends on regular house current, a power failure will leave this pump inoperative). If no drain is available, you can buy from Sheltech special reinforced plastic bags (made of pool-liner material) into which the water can be drained.

The three-valve Freeze-Gard System costs about $190, but the installer will have to purchase a number of vacuum breakers that must be installed at various points in the system (sold in all plumbing supply houses). These are needed to let air enter the pipes so they will empty quickly when the drain ports are opened.

The manufacturer furnished a detailed installation manual aimed primarily at the professional plumbing contractor, although it is written in simple language so that anyone familiar with a home plumbing system will easily understand it. However, unless the do-it-yourselfer has had more than an average amount of experience doing his own plumbing, it is best to have a licensed plumbing contractor do the job.

Labor costs will vary, depending on the size and layout of the house, but for most homes the cost will be from $150 to $250 for the labor and the additional fittings needed.

(Note: This system does not drain water traps under sinks and inside toilet bowls or tanks, although the same company is developing a simple device that will add antifreeze to these traps and the toilet tank when the house will be empty and without heat.)