Tank flushing delay arrangement for a steam generator

In a steam generator having a tank with a water inlet valve, a steam outlet, and a normally closed drain valve,

• a heater for said tank,
• a water level control for said inlet valve, said water level control arranged to maintain the water level in said tank between minimum and maximum levels, said water level control permitting power to be applied to said heater only when the water in said tank is above the minimum water level, and said water level control admitting make up water into said tank as steam is used from said outlet,
• the improvement comprising
• drain valve control means connected to said drain valve and operative to automatically open said drain valve for a predetermined flush period upon starting of said generator, and delay means cooperating with said drain valve control means to delay opening of said drain valve by said drain valve control means until the end of an elapsed cooling period sufficient to condense residual steam in said tank in the event of starting said generator promptly after shut down of said generator from a previous operation.

In a steam generator having a tank, a water inlet including an inlet valve connected to said tank, a steam outlet from said tank, a drain from said tank including a normally closed drain valve, and a heater for producing steam from water in said tank;

• the improvement comprising a control including
• means automatically opening said drain valve and said inlet valve upon starting said generator,
• means automatically closing said drain valve after a predetermined flushing period,
• means holding said inlet valve open until the water level in said tank reaches a predetermined level and continuing periodically to open said inlet valve to make up for lowering water level due to steam consumption,
• means energizing said heater in response to water reaching said predetermined level, and
• delay means inhibiting opening of said drain valve by said drain valve opening means until the end of an elapsed cooling period sufficient to condense any residual steam in the tank in the event that the generator is started shortly after shut down of the generator from a previous operation.

The method of operating a demand steam generator using a potable water supply, comprising

• heating potable water in a tank to its vaporization temperature and using the resulting steam for cooking or sterilizing,
• replenishing the water in the tank according to the demand for steam,
• upon shut down of the generator retaining a predetermined amount of water in the tank to keep minerals in suspension,
• automatically flushing retained water from the tank upon start up only if a predetermined cooling period sufficient to condense residual steam in the tank has elapsed following the last preceding shut down.