Boiler Feed Control Methods
Grundfos Centrifugal CR pumps

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In steam boilers, a constant water level is the key to reliable operation and high steam quality. There are several ways of controlling the amount of water in the boiler. Below we will describe 4 boiler feed control methods and explain the most efficient approach for level control in steam boilers.

Boiler Feed Pump Checklist

The first strategy, which is also the most straightforward, involves regulating the water level by toggling feed pumps on and off, guided by input from a level switch. As soon as the water reaches the designated level, the pumps are promptly activated, introducing substantial volumes of water into the boiler. While this method is cost-effective, it does come with its set of limitations.

The sudden rush of cold water leads to a decrease in both steam quantity and pressure, resulting in fluctuations in steam production. Additionally, temperature variances induce thermal stress, consequently diminishing the system's lifetime. Also, the frequent on-off cycles place significant strain on the pumps.

On/Off Control with fixed speed pump

Feed Valve with fixed speed pumps

To address these issues, one effective approach involves controlling the water level using a feed valve, which is managed by a boiler-installed level sensor. This feed valve allows a specific volume of water to enter the boiler, aligning with the current steam consumption. The outcome is a consistent water level and a steady steam pressure maintained consistently.

However, this approach requires the continuous operation of the feed pumps. To prevent shaft seals from overheating, a bypass loop must be installed. This adjustment increases energy consumption as the pumps are required to circulate an excess amount of water throughout the system, surpassing the actual need to maintain the right level in the boiler.

The valve itself presents its own set of issues. Its maintenance is costly and it contributes to pressure losses, which further increases energy consumption. In fact, a rough estimate suggests that a valve can add 25% to your energy expenses when compared to systems that don't incorporate valves.

In order to reduce this pressure loss, a third approach combines the feed valve with variable speed pumps, such as the CRE series pumps.

These variable speed pumps adapt their performance based on input from a pressure sensor in front of the feed valve, effectively minimizing the differential pressure across the feed valve. This leads to a reduction in energy consumption during pump operation. However, this strategy still relies on a bypass system and a feed valve to control the water level.

Feed Valve with Variable Speed Pumps

There is the fourth alternative strategy. By using the variable speed pumps to control the water level directly, feed valves become redundant and without the feed valve, there is no need for a bypass. The pumps seamlessly adapt their performance in response to demand, delivering smooth operation, simplifying the system, and providing significant energy savings.

In fact, for a boiler system generating 20 tons of steam per hour at 16 bar, experiencing a 5-bar pressure drop across the feed valve at 100% boiler load and following a standard load profile, the annual energy savings surpass 20,000 kilowatt/hours. Additionally, you'll have the flexibility to select a pump with fewer stages and a smaller motor since the pump no longer needs to compensate for the pressure loss caused by the valve. Overall, the energy savings of direct boiler feed are equal to the cost of a new expensive feed valve, including annual maintenance.

Variable Speed Pumps Less Feed Valve

To summarize, there are four main control strategies to regulate the water level in a steam boiler.

The on-off approach, while cost-effective, reduces both system lifetime and the quality of steam production.
The feed valve ensures steady operation but increases energy costs due to pressure loss across the valve.
The feed-valve-variable-speed pump combination reduces pressure loss, yet it still relies on costly feed valves and bypass systems.
But the most efficient level control in steam boilers is the incorporation of intelligent variable speed pumps which allow the smooth operation of the valve strategy with the simplicity and efficiency of the on-off system with lower capital costs and great energy savings as a result.


Method name	Uses a feed valve?	Pump Speed Type	Duty	Is orifice flow by-pass line required?
1. On / Off control and fixed speed pumps	No	Fixed	Intermittent	No
2. Feed control valve and fixed speed pumps	Yes	Fixed	Continuous	Yes
3. Feed control valve and variable speed pumps	Yes	Variable	Continuous	Yes
4. Variable speed pumps only (no control valve)	No	Variable	Continuous	No

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Boiler Feed Control Methods Grundfos Centrifugal CR pumps

Boiler Feed Control Methods
Grundfos Centrifugal CR pumps