Engineering Projects/Igloo/Howard Community College/Fall2012/p1-502-lash/test

Safety Warning
*** SAFETY WARNING - Before attempting to operate the pressure washer or conduct this test, read the pressure washer manual and the safety procedures page that our team developed ***

Overview
This team was planning to test the quality of the pressure washer hose splice by pumping it up to its full rated pressure and checking for joint failures and pinhole leaks. We were planning to use the garden hose spigot outside on the HCC plant ops dock as a water source, and a nearby outdoor electrical outlet for power. We were planning to use one of the dumpsters as a protective barrier between the operator and the test equipment. We were planning to use a video camera and remote monitor to view both the test process and the pressure gauges so that we could use conventional gauges instead of obtaining ones capable of sending a signal over a wire to a remote unit. Basically, the gauges would be put in view of the camera, with the test equipment visible in the background. Following is a description of a system we designed for testing the hose. All apparatus and test procedures the next team decides to use will have to be approved both by the professor and by HCC Plant Operations, because the test, as we envision it, will require use of Plant Ops equipment and workspace.

Schematic

 * The picture below is a hydraulic schematic of a possible arrangement of equipment for the hose pressure test. The link in the caption is to an electrical schematic for a possible remote control console. The nature and purpose of the components, as well as theory of operation, is explained below the image.  For information on reading hydraulic schematics, see:


 * article by user Suvo at brighthubengineering.com


 * hydraulic schematic symbols tutorial at solenoidvalvesuk.com (especially the graphic at the bottom explaining the solenoid valve symbol elements)


 * Jim Pytel's video tutorial on hydraulic system components and symbols



Component Description

 * 1: solenoid valve for water intake (normally closed) - This is to assure that no pressure is available to input side of the system prior to approaching the setup. This could probably be omitted with little increased risk, as the manual says to turn the water on before installing the spray tip, and to turn it off only when putting the washer away.


 * 2: intake water flow meter - This is because the manual says that at least 2 GPM flow rate should be available to the water inlet.


 * 3: inlet water pressure indicator - This is to assure that water is supplied to the washer at a pressure between 40 and 80 PSI, as called for by the manual.


 * 4: high pressure pump - This is the schematic representation of the pressure washer's pump.


 * 5: electric motor - This is the electric motor built into the pressure washer.


 * 6: output pressure gauge - This is included because epowerwash.com's article, How To Extend The Lifetime Of Your Pressure Washer Hose says "damaging pressure buildup could occur if the spray gun is shut off while the pump is still running," and we were planning to pressurize the hose with the drain valve closed, equivalent to the spray gun being shut off. A pressure gauge will allow the operator to see the pressure applied to the hose, and cut motor power and open the drain valve in the event of an overpressure condition.  While the total stop system built into the pressure washer should prevent an overpressure condition, it should not be relied on at least until its correct operation and calibration have been established.


 * 7: High pressure solenoid valve (normally open) - This is to depressurize and drain the system from a distance so that it is safe to approach and work on.

Theory of Operation

 * (copied from description on image file page)


 * Water enters through normally closed solenoid valve (1) and passes through intake flow meter (2) to high pressure pump (4). Intake water pressure is monitored by pressure gauge (3). The hose to be tested connects between pump (4) and normally open solenoid activated drain valve (7). To test the hose, pump drive motor (5) is turned on, the solenoid of drain valve (7) is activated, closing the valve, and the pump is run to pressurize the hose. Test pressure is monitored by gauge (6). When the test is complete or the hose fails, the solenoid of drain valve (7) is deactivated, opening valve and discharging water, depressurizing the system. All components are operated electrically by a remote control circuit so that the operator may perform the test from a protected location, monitoring it with a camera and video monitor.

Parts List

 * Quantities are 1 each unless otherwise specified.


 * solenoid valve, normally closed, 80 PSI, min. 2 G.P.M
 * water flow rate meter, 0-5 GPM, 80 PSI
 * water system pressure gauge, 0-100 PSI
 * water system pressure gauge, 0-2200 PSI (yes, two thousand, two hundred)
 * solenoid valve, normally open, 2200 PSI (GPM should match press. washer output)
 * fittings, adapters, and splitters appropriate for attaching valves and gauges to hoses
 * a garden hose to connect to the water source
 * a sawhorse or other device to which to firmly attach the hoses to prevent hose whip in case of failure
 * rope, wire, or other materials with which to secure the hoses to the saw horse/hose anchor
 * a remote control console (see below)
 * personal protective equipment, such as goggles, gloves, and heavy clothing
 * the pressure washer and hose

Ideal properties

 * it would allow operation of the inlet and outlet water valves and the pump motor power from a remote location


 * it would indicate the input and output pressure of the system, the input water flow rate and whether or not the motor is running


 * it would have fail safe indicator lights that either show the pressure to be live, relieved, or in case of a component failure, would create a condition that immediately alerts the operator to a problem


 * it would monitor pressure at several points (ideally, an infinite number of points) in the system, such as hose on either side of the splice and at the pump, indicate an unsafe condition if one or more points has pressure, and safe only if all points read low or no pressure


 * It would meet safety standards such as the National Electrical Code or those published by the National Electrical Manufacturer's Association.


 * it would use on shelf or readily available components


 * the controls would be arranged in a way that correct operation would be intuitive, requiring little to no written explaination.


 * it would be compact, light weight, simple to construct, and have low cost of materials


 * it would be aesthetically outstanding (polished chrome trim on gauges, moulded edges, attractively painted or finished wood construction, etc.)

Electrical Schematic

 * This Schematic is for one possible design of control console. Switches SW1 - SW3 control the solenoid valves and pump motor, and could be household light switches, or nearly any other type capable of delivering the current needed by the pressure washer's motor and the solenoid valves selected for water flow control.  LED's D1-D3 indicate the power status to various elements of the test equipment, and D4 is a power on indicator for the remote control.  Resistors R1-R4 (100 ohms in picture) are series current limiting resistors for the LED's, whose resistance will need to be chosen based on the LED current draw.  The power dissipation will likely exceed the standard resistor rating of 1/4 watt, so this will need to be considered when selecting resistors.  Multiple resistors could be used in series or parallel to increase the total dissipation capability.  An alternative would be to use light bulbs rated for 120 volt operation, separate step down transformers to drive each LED or light bulb, or a single voltage bucking transformer between the LED return wires and the neutral bus to reduce the total voltage available.  If at all possible, the unit should be plugged into a ground fault circuit interrupter equipped outlet.

Parts List

 * household light switches                Qty: 3  (should be available in engineering lab parts stock)


 * LED's or other indicator light device   Qty: 4  (should be available in eng. lab stock)


 * limiting resistors for LED's              Qty: 4 (they are available in stockroom, CL 160)
 * general purpose rectifyiing diodes, such as 1N4004, to limit reverse voltage on LEDs   Qty: 4
 * A panel to mount the parts on, or suitable enclosure
 * hookup wire (should be 14 gauge minimum size)
 * a ground fault circuit interrupter socket  Qty:1
 * hardware with which to mount the electrical components on the panel or in the enclosure
 * an outdoor use rated extension cord, minimum wire size 14 gauge, to plug the remote unit into the wall  Qty:1