February 1, 2002
Pumpgard Safety System
If you are responsible
for progressive cavity pumps that are used for the delivery of emulsion
explosives, no doubt you have heard of our PumpgardÔ Safety System. Over
500 of these systems have been manufactured and installed since their
introduction in 1993. Tread Corporation has been made aware of an
instance where the Pumpgard Safety System was misused. This safety
bulletin is intended as a further warning and instruction against misuse and/or
operation of the system. The details of this occurrence are as follows.
A twin-tank emulsion repump truck was being off-loaded into an overhead
storage bin using the progressive cavity pump on the truck. One emulsion
tank was empty and the second was partially full. The operator
incorrectly opened both tank valves before beginning the operation. With
the pump inlet open to atmosphere through the empty tank, the pump could not
develop suction, and little or no product flowed through the pump. This created
a potentially hazardous run-dry condition.
Pumpgard incorporates two devices, a low-pressure switch and a flow
switch, to detect a run-dry condition. In this case, the low-pressure switch
was not functioning properly and the flow switch had been by-passed in an
ingenious way that fooled the Pumpgard logic controller. With both of the
redundant run-dry safety devices inoperable, the pump ran unabated until the
Pumpgard run timer tripped after 10 minutes. At this point, Pumpgard had
done its job, and a potential pump-hazard event had been avoided.
Unfortunately, the operator was unaware of the potential danger of the
situation. He manually reset the Pumpgard timer and continued to run the
pump. After several consecutive 10-minute pump runs, the operator stopped
the pump in response to a high-pressure event that ejected the hose from the
barbed fitting at the outlet of the pump. Subsequent examination of the
pump showed extreme temperature effects on both the rotor and stator along with
visible product degradation.
Fortunately, this incident ended without a catastrophe and the full chain
of events could easily be reconstructed. I would like to draw on this
incident to illustrate a four-step program for managing pump safety that would
have prevented this pump-hazard event from occurring.
Operator training. Every pump truck operator
should receive annually recurrent training in the hazards of pumping emulsion
explosives, and the operation of the pump safety system.
Daily checks. Each operator should verify the correct operation of
the safety devices daily. Pumpgard includes indicator lights that show
the state of the devices.
Responsible maintenance. The pump safety system
must be responsibly maintained. Any defective devices should be
expeditiously repaired or replaced. It is never acceptable to by-pass a
safety device.
Quarterly re-qualification. The full and correct
function of the safety system should be verified and signed off by a
responsible company official on a quarterly basis.
If these four steps had been followed prior to the incident above, the
pump-hazard event would never have occurred. The operator would have
understood how to correctly perform the off-load operation. His daily
check would have informed him that the low-pressure switch was not
functioning. He would have understood the potential hazard of continuing
to reset and run the pump. And, even if the flow switch had been
by-passed, it would have been discovered in the last quarterly re-qualification.
Attached to this safety bulletin are two additional documents. The
first is a Recommended Safety Program that incorporates the four steps listed
above. The second is our Recommended Minimum Functionality for a
pump safety system. We strongly urge everyone that is responsible for the
operation of progressive cavity pumps used for the delivery of emulsion
explosives to follow these recommendations.
Copies of these documents should be placed in the front of each Pumpgard
operating manual, and all personnel involved in the operation and/or
maintenance of Pumpgard systems should be appropriately re-trained. Tread
Corporation is available to assist you in implementation of the Recommended
Safety Program and the training of your operators and technicians in order to
assure safe operation and effective maintenance of your pump safety systems.
Please feel free to contact Tread Corporation if you have any questions
at all about pump safety systems or operator training.
Best regards,
Dave Cole
Engineering Manager
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Insert this page in the front of all Pumpgard Operating Manuals
Pumpgard Safety System
Recommended Safety Program
The Pumpgard Safety System is designed to quickly stop a progressive
cavity pump if either a run-dry or dead-head condition is detected while
pumping emulsion explosives. A conscientiously administered safety
program should accompany the installation of the safety system to ensure that
it continues to provide the required level of protection.
The following four-step program is recommended.
Operator training. Every pump truck operator
should receive annually recurrent training in the hazards of pumping emulsion
explosives, and the operation of the pump safety system. Tread
Corporation can supply operating manuals and training materials for this
purpose.
Daily checks. Each operator should verify the correct operation of
the pump safety devices on a daily basis. Pumpgard includes indicator
lights that show the state of the devices, and to indicate any condition that
triggers a shut-down. Refer to the operating manual for an explanation of
these devices and their operation.
Responsible maintenance. The pump safety system
must be responsibly maintained. Any defective devices should be
expeditiously repaired or replaced. It is never acceptable to by-pass a
safety device.
Quarterly re-qualification. The full and correct
function of the safety system should be verified and signed off by a responsible
company official on a quarterly basis.
These recommendations are made in consideration of the level of the hazard that
may develop if either a run-dry or dead-head condition is allowed to continue
unchecked. Both of these conditions can produce dangerously high
temperatures inside a progressive cavity pump, which may ultimately result in a
catastrophic pump-hazard event.
Because Pumpgard stops the pump when it first detects a run-dry or dead-head
condition, the trip-off action occurs well before a dangerous hazard is allowed
to develop. Consequently, it is often seen as a nuisance. Often,
the nuisance trip is simply the result of a misadjusted flow switch, which
could be easily corrected by a properly trained operator. However, a
frustrated operator may be tempted to bypass the safety system to eliminate
this nuisance. This action should be prevented.
WARNING: NEVER ATTEMPT TO BY-PASS THE PUMPGARD SAFETY SYSTEM.
SERIOUS INJURY AND PROPERTY DAMAGE MAY RESULT.
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Insert this page in the front of all Pumpgard Operating Manuals
Pumpgard Safety System
Recommended Minimum Functionality
The Pumpgard Safety System is designed with redundant safety devices to
detect the onset of potentially hazardous conditions during the operation of
progressive cavity pumps. The hazardous conditions that can occur when
pumping emulsion explosives are any conditions that may result in temperatures
rising to a dangerous level.
1. Run-dry condition. The condition where
the pump is running without product supplied to the inlet. Pressure at
the outlet is near zero, and there is no flow of product through the
pump. Friction between the dry rotor and stator can generate heat inside
the pump where temperatures can rise to a dangerous level.
2. Dead-head condition. The condition where
the pump is running with the outlet blocked. Pressure at the outlet rises
to the maximum capability of the pump, and there is no flow of product through
the pump. All of the input horsepower provided by the motor driving the
pump is absorbed inside the pump where temperatures can quickly rise to a
dangerous level.
The following minimum set of devices is used with Pumpgard to detect the
run-dry and dead-head conditions, and to prevent the build-up of heat inside
the pump.
Redundant devices are used to ensure a higher level of safety. For
example, if the low-pressure switch fails to operate, the flow switch provides
redundant run-dry protection. Likewise, if the high-pressure switch fails
to operate, the burst disc provides redundant dead-head protection.
TREAD CORPORATION INSTALLS THIS MINIMUM SET OF SAFETY DEVICES IN THE PUMPGARD
SAFETY SYSTEM TO PROVIDE REDUNDANT PROTECTION AGAINST POTENTIAL PUMPING
HAZARDS.