Method and apparatus for supplying feedwater to a forced flow boiler

In a feedwater control system for supplying water to forced flow boilers, steam generators and the like wherein the fuel to a burner is controlled in accordance with the quantity of steam desired and water required by the boiler, the combination which comprises:

• (a) a positive displacement pump for pumping water betwen an inlet and an outlet, the pump having a plurality of discrete pumping elements, each pumping element having a water chamber connected between the inlet and outlet, a piston and cylinder, a first chamber containing a supply of pumping fluid, a second chamber and a flexible diaphragm connected between the second chamber and the water chamber, the piston being arranged to pump fluid from the first chamber through the cylinder and into the second chamber whereby the diaphragm is moved to displace water within the water chamber to pump a predetermined quantity of water from the inlet to the outlet for each complete cycle of the piston, the pump further including a bypass valve individually associated with at least some of the pumping elements, the bypass valve being constructed and arranged to connect the first and second chambers when open to thereby prevent movement of the diaphragm of the associated pumping element, and
• (b) control means for monitoring the fuel flow to the burner for alternately opening and closing at least one of the bypass valves at a periodic rate with the open to closed time bearing a relationship to the fuel flow rate.

The method of supplying feedwater to forced flow boiler, steam generator or the like, wherein the fuel to a burner for heating the water within the boiler is controlled in a continuous manner in accordance with the quantity of steam desired and wherein a positive displacement pump having a plurality of discrete pumping elements is connected between the boiler and a source of feedwater to provide water to the boiler, comprising:

• (a) monitoring the rate of fuel flow to the burner to determine the water flow rate required by the boiler;
• (b) operating the feedwater pump;
• (c) disabling a selected number of the pumping elements so that the rate of water supplied by the remaining elements, if operated continuously, would just exceed that required;
• and
• (d) disabling at least one of the remaining pumping elements on a periodic basis so that the ratio of the time that the element is enabled to the time for one period multiplied by the water flow rate supplied said element, if operated continuously, equals difference between the total demand rate for water and the rate supplied by the remaining pumping elements enabled on a full-time basis.

The method of supplying feedwater to forced flow boiler wherein the flow of fuel to a burner is controlled in a continuous manner in accordance with the quantity of steam desired and wherein a positive displacement pump having a plurality of discrete pumping elements is connected between the boiler and a source of feedwater, the pump having means associated with each pumping element for selectively disabling the pumping action of said element, comprising:

• (a) monitoring the rate of fuel flow to the burner to determine the water flow rate required by the boiler;
• (b) operating the feedwater pump to supply water to the boiler;
• and
• (c) disabling at least one of the pumping elements on a periodic basis with a variable duty cycle, the duty cycle bearing a relationship to the demand for water.

The method of supplying feedwater to a forced flow boiler wherein the flow of fuel to a burner is controlled in a continuous manner in accordance with the quantity of steam desired and wherein a positive displacement pump having a plurality of discrete pumping elements is connected between the boiler and a source of feedwater, the pump having means associated with each pumping element for selectively disabling the pumping action of said element, comprising:

• (a) determining the water flow rate required by the boiler;
• (b) operating the feedwater pump to supply water to the boiler;
• and
• (c) disabling at least one of the pumping elements on a periodic basis with a variable duty cycle, the duty cycle bearing a relationship to the demand for water.