Automatic or Remote Starting of Pumps

1. Purpose

This procedure provides guidelines for starting motor and turbine driven pumps automatically or remotely.

2. Motor Driven Pumps

2.1 Torque Requirements

When a motor accelerates from a standstill to normal operating speed, it must produce enough torque to exceed the pump’s torque requirements by an amount that provides enough net torque to accelerate the motor and pump in a reasonable amount of time.

2.2 Normal Start-up

Normally, close the isolation valve in the pump discharge line before starting the motor which minimizes the pump’s torque requirements and prohibits flow through the pump until the motor reaches operating speed.

In some cases, however, motor driven pumps may be started with the discharge valve open.

2.3 Problems with Acceleration Torque

The significance of the acceleration torque problem varies with each system.

a. High Static Systems

Acceleration torque is a minor problem in high static systems where the pressure against the pump check valve at start-up almost equals the normal discharge pressure. These systems allow the pump to accelerate to a speed near its normal operating speed without permitting flow through the pump.

b. Low Static Systems

Acceleration torque is a major problem in low static systems where the pressure against the pump check valve at start-up is much lower than the normal discharge pressure. Low static systems allow flow through the pump soon after the pump begins to rotate.

2.4 Spillback Valve Open

As the operating pump winds down and when the non-operating pump is on standby or auto start with the discharge isolation valve open, consider if the flow control instrumentation will open the spillback valve. If the spillback goes open, the pump discharge will see the suction pressure rather than the destination pressure plus the static head. Therefore, ensure that the motor provides enough torque to accelerate the pump against the suction pressure. In this instance the motors for multi-stage pumps, will need to be large, as is the case for a set of boiler feedwater pumps with spillbacks.

2.5 Torque Capabilities

If motor driven pumps are equipped with automatic starting devices, or they are started remotely include the following note on the motor page of the pump specification:

"Motor shall have the torque capability to accelerate the pump to operating speed with the discharge shutoff valve open and the discharge check valve closed against a static pressure of psig."

Fill in the minimum pressure downstream of the discharge check valve at no flow. This is typically the destination pressure plus the static head. This minimum pressure requires the most starting torque in the motor.

Do not consider the torque requirements of pumps on loading systems that have set-stop valves which are equipped with back pressure sensing pilots. The set-stop valve will not open until the discharge pressure developed by the pump is near the normal operating level.

Additionally, do not consider the torque requirements of pumps on any system in which the pumps may be started remotely and the operator can easily close a valve in the pump discharge line. Simply assume that the operator will close the valve prior to start-up like a locally started pump.

If, however, the pump shutoff valve is not conveniently located by the remote push-button station, assume that the operator will not close the discharge valve. Take the steps necessary to assure that the motor meets the required starting capabilities.

3. Starting Steam Turbine Driven Pumps

Turbines are essentially constant torque devices. Thus, there is no need to consider the driver torque capabilities of steam turbine driven pumps. There are, however, two other special requirements.

a. Open the exhaust steam isolation valve on turbines that are connected to an exhaust steam system. Equip the low point (either the exhaust or the turbine case) with a suitable steam trap. Equip turbines that exhaust to the atmosphere with an open drain at the low point.

b. Seat the shaft seal rings by slowly idling the steam turbines that are maintained in a standby condition with exhaust steam pressure on the case. To assure adequate lubrication and avoid startup problems, consider the idling requirements of geared turbines and other special equipment items. Follow the vendor's recommendations.

Idling turbines also require, in addition to the low point steam trap, a small inlet control valve by-pass (usually a 3/4" or 1" globe valve).

Include the following note on the steam turbine page of the project specification:

"Turbine shall be suitable for automatic start."