Cleaver Brooks Model 5 750-154 FLX Maintenance

Cleaver Brooks Model 5 750-154 FLX Maintenance

Water Level Controls

Open — 190º F

Open — 180º F
Close — 170º F

Open — 170º F (low fire)
Close — 165º F (high fire)

Source: Cleaver Brooks

Water Level Controls

The water level control has 2 float actuated mercury switches. One switch is connected to the burner limit circuit and will stop the burner if a low water condition occurs. On a steam boiler the other switch is connected to the feedwater circuit to energi

The control is of the automatic reset type and will remake the limit circuit when the water level is restored. Some applications require that a control be equipped with a manual reset mechanism that must be manually reset before the burner can be restarte

Low water cutoff devices are generally set by the original manufacturer and no attempt should be made to adjust these controls to alter the point of low water cutoff or point of pump cut-in or cut-out. If a low water device should become erratic in operat

The need to periodically check water level controls cannot be over emphasized. Most instances of major boiler damage are the result of operating with low water.

On steam boilers the head mechanism of the low water cutoff device(s) should be removed from the bowl at least once a month to check and clean the float ball, the internal moving parts, and the bowl or water column.

In addition and at the same time, remove the pipe plugs from the column, tees or crosses to make sure the cross connecting piping is clean and free of obstructions. Controls must be mounted in a plumb position for proper performance. Determine that piping

Water level controls normally function for long periods of time which may lead to laxity in testing on the assumption that normal operation will continue indefinitely.

Testing of the controls, especially on steam boilers, should be followed on a definite planned schedule. The control’s operation may be checked by stopping the water supply to the boiler while the burner is operating at low fire.

While under constant attendance allow the water to lower at a normal rate. If a control does not break the circuit to stop the burner at the proper point then SHUTDOWN THE BURNER IMMEDIATELY. Repair or replace the control at once.

A scheduled blowdown of the water controls on steam generators should be maintained.

On a hot water boiler it is impractical to perform daily and monthly maintenance of the low water cutoff devices. However, it is essential to remove the operating mechanism from the bowl annually or more frequently, if possible, to check and clean the flo

Also check any cross connecting piping to make certain that it is clean and free of obstruction. It is not practical to blowoff or drain the low water cutoff devices, since the entire water content of the system would become involved. Many hot water syste

Water Gauge Glass

A blowdown cock is provided on the lower gauge glass fitting and a daily blowdown is recommended. The glass should be removed every 3 months and checked, while cool, for etching, thinning, or damage. If any defects are found, replace the glass immediately

Do not over tighten water gauge glass fittings. Check try cocks and gauge cocks for freedom of operation and clean as required. Proper alignment of gauge glass cocks is essential to prevent mechanical strain on the glass.

Operating Controls

The following instructions apply to those controls considered standard, or normally provided as optional. Space prevents listing other controls or variations of those listed that may be included in the circuitry due to job specifications or insurance carr

In general, when adjusting controls check to see that they are level, especially those containing mercury switches. On temperature sensing controls make sure that the bulb is properly bottomed in its well. Make sure that connecting tubing is not kinked or

Controls are carefully calibrated during their manufacture and do not normally require recalibration. The dial settings are generally quite accurate although it is not unusual to have a slight variation between a scale setting and an actual pressure gauge

Most of the operating controls require very little maintenance beyond occasional inspection. Examine tightness of electrical connections. Keep controls clean. If any dust accumulates in the interior of the control, remove with a low pressure air hose taki

Examine any mercury tube switches for damage or cracks: this condition, indicated by a dark scum over the normally bright surface of the mercury, may lead to erratic switching action. Make certain that controls of this nature are correctly leveled using

Dust and dirt can cause excessive wear and overheating of motor starter and relay contact and maintenance of these is a requirement.

Starter contacts are plated with silver and are not harmed by discoloration and slight pitting. Do not use files or abrasive material such as sandpaper on the contact points since this only wastes the metallic silver with which the points are covered.

Use a burnishing tool or a hard surface paper to clean and polish contacts. Replacement of the contacts is necessary only if the silver has worn thin.

Setting and Adjusting

The Model 5 boiler is designed to withstand considerable change in steam pressure or water temperature, however, good operating practice with any boiler is to avoid thermal shock caused by rapid and frequent variations. Therefore, it is advantageous to se

Normal operation of the burner should be with the damper positioning switch in the “auto” position. This allows the burner to automatically shift from one firing rate to another in accordance with load requirements.

Burner Operating Controls: Gas

Burner controls properly set to match load demands will provide operational advantages and achieve the following desirable objectives:

The burner will be operating in low fire position prior to shutdown.

The burner will operate at low fire for a brief period on each start during normal operation.

eliminates frequent burner on-off cycling.

Operating and Modulating Control Actions

Figure 5-1 depicts a typical relationship of the setting of the operating limit control and the modulating control. Please note that this is not drawn to any scale. The burner will be “on” whenever the pressure or temperature is below point B and “off ” w

The distance between points A and B represents the “on-off ” differential of the operating limit control.

In normal operation, the burner will shut down whenever the pressure or temperature reaches setting A. The switch in the operating limit control will open. As the pressure or temperature drops back to B, the switch makes and the burner will restart.

The modulating control will be calling for the modulating motor to be in a low fire position at this point. If the load exceeds this low fire input, the modulating control will respond to increase the firing rate proportionately as pressure or temperatur

Point D represents the maximum firing rate of the burner. In the event pressure or temperature drops while the burner is firing at its maximum input, this is indicative that the load exceeds the generating rate of the boiler.

Although a gap is shown between B and C, these points may well coincide if required by load conditions. When set as shown, the burner will be in a low fire position upon a restart and will fire at that rate for a short period of time before falling pressu

From this illustration it can be seen that this desirable objective will not be attained if setting C overlapped point B. In that event, upon a restart, the burner would drive to a higher firing position immediately after main flame was proven, and the br

When firing a cold boiler, it is recommended that the burner be kept under manual flame control until normal operating pressure or temperature is approached. The size of the flame may be manually and gradually increased to build up pressure or temperature

This rapid heat input can subject the pressure vessel metal and refractory to undesirable conditions. A 10 minute low fire hold is incorporated to slow this rapid heat input.

Any control setting must not cause the boiler to operate at or in excess of the safety valve setting. Settings that do not exceed 90 percent of the valve setting are recommended, with lower settings greatly desirable if load conditions permit. Avoid havin

Continued leakage, however slight, will cause erosion and necessitate early valve replacement. The control settings on a hot water boiler must be within the temperature and pressure limits of the boiler.

Ideally, the burner operating controls should be set under actual load conditions. Often, especially on new construction, the boiler is initially started and set to operate under less than full load requirements. As soon as possible thereafter the control

To accomplish this, and assuming that air/fuel combustion ratios have been set, make approximate adjustments to the controls to bring the boiler pressure or temperature up to meet the load requirements.

To properly set the modulating control, carefully adjust it under load conditions, until the load is maintained with the burner firing at a steady rate. The firing rate at that point may be full high fire or slightly less, depending upon the relationship

When the modulating control is set in this manner and if the burner is in full high fire, the scale setting of the modulating pressure control on a steam boiler will have a reading that indicates the low point of the modulating range. T

This fixed differential range is described later in this section. The scale setting of the modulating temperature control on a hot water boiler will have a reading that indicates the midpoint of the modulating range. This is also described later.

The operating limit control should now be adjusted and its differential established. See directions later in this section for the mechanics of adjusting. In an installation that does not require a very close control of steam pressure or water temperature,

The high limit control provides a safety factor to shut the burner off in the event the operating limit control should fail to do so. The setting of this control should be sufficiently above the operating limit control to avoid nuisance shutdowns

The setting, however, must be within the limits of the safety valve settings and preferably not exceed 90 percent of the valve setting. The control requires manual resetting after tripping.

In the setting of these controls, consideration must be given to the time required for a burner restart. Upon each start, there is a pre-purge period of some length, plus the fixed time required for the proving of the pilot and main flame.

This, plus approximately one-half minute required for damper motor travel from low to high fire, may allow pressure or temperature to drop below desirable limits.

Pressure Controls: Steam Boiler (Oil)

The pressure controls that serve as the operating limit control and as the high-low fire control are equipped with an adjustable differential setting. See the following portion of this section for adjustment procedures.

Basically, the switch in the control opens when the steam pressure reaches a pressure equal to the main scale setting and closes at a pressure equal to that shown on the main scale, minus the amount of differential.

In an installation that does not require very close control of the steam pressure, the differential setting should be adjusted to its maximum, since this will provide less frequent burner cycling.

The control settings should not cause a boiler to operate at or in excess of the safety valve setting. Control settings that do not exceed 90 percent of the safety valve pressure are recommended. Operation of the boiler very close to maximum valve setting

Continued leakage through the valve will cause erosion to its components and necessitate early replacement. Therefore, the steam pressure control should be adjusted to operate the boiler at the lowest pressure required to satisfy the load demand.

The high-low fire control should be set to open at 5 to 10 psi lower than the operating limit setting. The suggested setting on a low pressure steam boiler is 2 to 3 psi. The differential setting on this control may be set low, to give quite close control

In any case, the control should be adjusted so that it de-energizes the damper motor, causing the burner to go to low fire, at a pressure below the limit control opening point. When the pressure controls are properly set the burner will maintain steam dr

On a rise in steam pressure, the high-low fire control opens its contacts and the damper motor returns to low fire position. The burner continues to operate at low fire rate. If steam pressure drops, the control will again close to energize the damper mot

Should the boiler pressure reach the set point of the operating limit control, its contacts will open to turn off the burner.

When boiler pressure drops, the operating limit control contacts close, causing the burner to restart. It is desirable to have the high-low fire control adjusted so that the burner does not immediately go to high fire upon start, but rather operates at lo

Temperature Controls: Hot Water Boiler (Oil)

The temperature controls that serve as the operating limit control and as the high-low fire control are equipped with an adjustable differential setting.

Basically the switch in the control opens when the water temperature reaches a temperature equal to the dial setting and closes at a temperature equal to the dial setting minus the amount of differential. See the following portion of this section for inst

In an installation that does not require very close control of the water temperature, the differential setting should be adjusted as widely as possible since this will provide less frequent burner cycling.

The operating limit temperature control should be set slightly above the highest desired water temperature and within the limits of the pressure vessel.

The high limit control should be set 5 to 10 degrees above the operating limit temperature control setting. The high-low fire control should be adjusted so that it is below the burner “on” temperature of the operating control.

Relative settings of the temperature controls are as follows:

High Limit Control

Open — 190º F

Operating Limit Control

Open — 180º F

Close — 170º F

High-Low Fire Control (high fire)

Open — 170º F (low fire)