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HYDROLOGICAL SERVICES PTY LTD

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PRESSURE SYSTEM OF HEAD MEASUREMENT

GAS PURGE PRINCIPLE

The behaviour of a gas flowing under a variable back pressure is utilised as an accurate means
of measuring liquid head.

Provided that:

1. The density of the gas is nearly the same as air
2. The velocity of gas is low enough so as not to produce significant pressure drop            

      

down the line then the system pressure will be equal to the back pressure.

This principle is illustrated in the following series of diagrams.
In the first example, the tube exhausts to atmosphere and hence the water manometer indicate
zero
pressure in the system because it is acted on by two equal pressures- the system pressure and the
atmospheric pressure

Fig.1 - Depicts first stage in application of gas purge principle.

Fig.1 also illustrate another feature of all pressure systems, namely the gas endeavours to escape
through any material that it is in contact with to find a lower pressure, but for practical purposes,
the system pressure reflects the lowest of the outlet pressures. In this case, gas endeavours to
pass through the walls of the tubing and fittings, through the water, but elects to take the easier
path to atmosphere, which is in effect a “massive leak”.

Gas Purge Compressor

  

Issue 7: 

16/12/03

© Copyright

HS55 110-014

Содержание HS-55

Страница 1: ...ERVICES PTY LTD _______________________________________________________________________________________ INSTRUCTION MANUAL GAS PURGE COMPRESSOR MODEL HS 55 Gas Purge Compressor Issue 7 16 12 03 Copyright HS55 100 01 ...

Страница 2: ...II TESTING YOUR SYSTEM HS55 100 04 IV SPECIFICATION HS55 100 05 V INSTALLATION HS55 100 014 VI OPERATION HS55 100 017 VII MAINTENANCE HS55 100 018 VIII BUBBLE RATE ADJUSTMENT HS55 100 018 IX FAULT FINDING HS55 100 019 X DRILLING TEMPLATE HS55 100 019 XI APPENDIX A HS55 110 01 XII APPENDIX B HS55 110 08 XIII APPENDIX C HS55 110 013 Gas Purge Compressor Issue 7 16 12 03 Copyright HS55 100 02 ...

Страница 3: ...OMPRESSOR MODEL HS 55 The HS 55 incorporates a 3 Way switching valve for manual purging of the system Continuous purging occurs when the valve is rotated to Purge position This is similar to Dry Bubble Unit Model HS23 functions For instructions how to use the valve please refer to page 18 of this manual Auto Drain Moisture Trap The system features an Auto Drain Moisture Traps When the traps sense ...

Страница 4: ...ately 4 minutes to fill the air tank to maximum pressure of 85 p s i 600 Kpa and will then automatically switch off Connect to the outlet port see figure 6 a short piece of river line tubing and secure the end into a container of water Check the bubble rate setting as required factory setting is equivalent to 80 bubbles per minute If the bubble rate requires adjustment see page 16 for instructions...

Страница 5: ...tres 150 ft of water head with 100 metes 330 ft of river line Maximum Length River Line 200 Metres Using 3 8 O D x1 8 I D Tubing Maximum Purge Pressure 85 p s i 600 kpa Minimum Purge Pressure 60 p s i 400 kpa Differential Pressure 3 p s i 20 kpa to 5 p s i 35 kpa Purging Manual 3 Way Switching Valve Bubble Rate User selectable from 60 to 120 bubbles minute See page 16 for adjustment details Air Dr...

Страница 6: ...00 non condensing Overall Accuracy 0 02 F S BSL Long Term Stability Typically 0 05 F S annum Pressure Connection 1 4O Tube Sensor Vent Vent fitting for Hydrophobic Filters and or desiccant packs Calibration Over full range against water head Operating Voltage 9 6 to 16VDC operation ie from SDI 12 12 volt supply Current Loop Operating Voltage 9V to 30V DC for 4 20mA current loop drive used as a 2 w...

Страница 7: ...ring Output RS232 SDI 12 and 4 20mA output ii Pressure Transducer Model W L 2100 Dry Accuracy 0 05 B S L Operating Temp 20 deg C to 60 deg C 4 o F to 140 o F Combined non linearity Hysteresis and Repeatability 0 05 of full scale Long term stability 0 03 full scale per annum Compensated temp Range 20 deg C to 60 deg C 4 o F to 140 o F iii Pressure Line 1 8 I D x 3 8 O D heavy wall black polyethylen...

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Страница 14: ...mpressor at the top A mounting bracket can be provided for bench mounting see drilling template page 17 ii Connect your pressure sensor directly to the manifold or connect a pressure line between the manifold and your pressure measurement device If your measurement device has non compatible connections you will need to request adaptor fittings to suit The manifold port for the transducer is BSP ii...

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Страница 18: ...ny leak will allow the entire gas flow to escape VIII BUBBLE RATE ADJUSTMENT The chart below has been prepared to show the relationship between the bubble rate at the test orifice and the equivalent rates that would be observed on a sight glass bubble unit Once the desired bubble rate has been achieved tighten the screw to lock the metering valve Bubble rate at Equivalent Sight Test Orifice Glass ...

Страница 19: ...b Check all connections including POWER and GROUND Both the compressor and control power sources must be connected ii Intermittent Operation C Check your power and ground connection Moisture over time will oxidize and corrode connectors and pins C Verify your power supply or battery voltage X DRILLING TEMPLATE See page 20 Gas Purge Compressor Issue 7 16 12 03 Copyright HS55 100 019 ...

Страница 20: ...HYDROLOGICAL SERVICES PTY LTD _______________________________________________________________________________________ Gas Purge Compressor Issue 7 16 12 03 Copyright HS55 100 020 ...

Страница 21: ...HYDROLOGICAL SERVICES PTY LTD _______________________________________________________________________________________ XI APPENDIX A Gas Purge Compressor Issue 7 16 12 03 Copyright HS55 110 01 ...

Страница 22: ...ice mounting should be such that it can withstand the forces applied by the flowing stream and associated floating debris C Preparation of Orifice Tubing Do not open the carton or remove the strapping To prepare the roll of tubing for use cut a 300 mm diameter hole in the centre of the cardboard carton retrieve the end of the tubing from the middle of the coil then cut the strapping retaining the ...

Страница 23: ...nsure that it is free of coils and kinks Under no circumstances should the tube form hollows where moisture can be trapped within the tube Lay the tubing into position in the equipment shelter as required Remove the protective tape from the end of river line tube Insert the end of the tube into the appropriate river line fitting on the HS55 and tighten both fittings Refer to diagram for tightening...

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Страница 25: ...HYDROLOGICAL SERVICES PTY LTD _______________________________________________________________________________________ XII APPENDIX B Gas Purge Compressor Issue 7 16 12 03 Copyright HS55 110 08 ...

Страница 26: ...n be used on fast rising water levels thereby reducing gas consumption by as much as 60 The GC01 chamber orifice is constructed of copper and welded to a 2 copper connection The connection mates with a 2 plastic insulating bush and is taped for a 1 4 National pipe thread NPT copper Swagelok a fitting which allows adaptability to the existing standard USGS orifice configuration The bottom of the ch...

Страница 27: ...the ingress of dirt etc from entering the tubing by taping up the ends At no time should the open end of the tubing be permitted to contact the soil I Orifice Tubing It is recommended that a trench be dug minimum 600 deep between the equipment shelter and the proposed positions of the orifice The trenches should not have any low points in their length they should have a continuous fall to the rive...

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Страница 33: ...In the first example the tube exhausts to atmosphere and hence the water manometer indicate zero pressure in the system because it is acted on by two equal pressures the system pressure and the atmospheric pressure Fig 1 Depicts first stage in application of gas purge principle Fig 1 also illustrate another feature of all pressure systems namely the gas endeavours to escape through any material th...

Страница 34: ...of gas through the line resulting in a pressure between valve A and the outlet Depending on the location of the manometer connection the manometer will reflect a proportion of this increase in pressure Fig 2 High gas flow Refer Bubbler System Instrumentation for Water Level Measurement Report of Investigation No 23 state of Illinois U S A Head To Pressure Conversion As we are not seeking to measur...

Страница 35: ...he pressure of each bubble of gas as it emerges from the end of the tube will a that point have an internal pressure equal to the head and this internal pressure reduces until the bubble emerges at the surface at atmospheric pressure Therefore the gas acts like a plunger to keep the water out of the tube and in effect precisely balances the head of water that would naturally occur if the tube was ...

Страница 36: ... the new head H2 but rather H2 x This condition will remain as long as the gas is shut off In other words we now have a closed system which respond to changes in accordance with universal gas law a constant PV T i i i To revert back to the open system we must restore gas supply which will eventually build up pressure in the system until the gas escape from the orifice and the system pressure again...

Страница 37: ...es Accordingly even the lowest bubble rate will suffice for falling conditions In practice it may take some time to the pressure to bleed away but this is usually less than the response time of the sensing unit Field Requirement of Gas Purge Systems The principle requirements of gas purge are 1 a fine metering valve and sight feed for accurately setting the bubble rate 2 Constant regulator to main...

Страница 38: ...to make the connection to the system near the orifice so in effect there are two lines running the orifice Hence the term dual line The operation of Hydrological Services units is described in more details in diagrams 15 and 16 of instruction Manual for Sherlock Pressure Sensing Units Pressure Bulb or Closed System The pressure bulb system relies on the normal constant relationship for gases under...

Страница 39: ...he water rises within the bulb This amount x is non linear and therefore cannot be completely compensated for by simple calibration Provided the head H does not fall below say 300 mm error from this cause is minimal Basically the closed system will give good results subject to gradual changes of water temperature being experienced and the system being completely gas tight A full discussion of this...

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