What is positive displacement move meter?
Positive displacement (PD) flow meters are move meters that provide excessive accuracy (±0.1% of actual circulate in some cases) and good repeatability (up to 0.05% of reading). These meters require no energy provide to operate and no direct upstream or downstream piping for set up. They are properly fitted to move measurement of viscous fluids, similar to oils, fuels and solvents, that are tough to measure with other types of flow meters.
PD flow meters are most widely utilized in home water meters, with millions of these units produced every year. Volumetric flow meters can be utilized for clear, sanitary and corrosive fluids similar to water and meals, as nicely as some gases. They are often most relevant when excessive accuracy at an affordable value is required.
How does a optimistic displacement circulate meter work?
Positive displacement move meter know-how is the only flow measurement know-how that instantly measures the volume of fluid passing through the meter. Volumetric flowmeters do this by repeatedly intercepting fluid to measure its circulate rate. This process can be regarded as repeatedly filling a bucket with fluid earlier than pouring the contents downstream. The variety of instances the bucket is crammed and emptied indicates the move fee via the flowmeter. There are many volumetric circulate meter geometries obtainable.
Retention is typically achieved using rotating parts that form a transferring seal between each other and/or the flowmeter physique. In most designs, the rotating parts have tight tolerances in order that these seals stop fluid from passing through the flowmeter without being measured (sloshing). In some volumetric flowmeter designs, bearings are used to help the rotating parts. Rotation could be sensed mechanically or by detecting the motion of the rotating parts. As more fluid flows, the rotating parts rotate proportionally faster. The transmitter processes the signal generated by the rotation to discover out the circulate rate of the fluid. Some volumetric flow meters have mechanical registers that present the total move fee on a local display.
Features
Suitable for smaller line sizes, low circulate rates, high viscosities and long durations, especially for oils. The disadvantages are that there are shifting parts to wear, maintenance required, more impurities, and not as updated as other technologies with new protocols, etc.
Accuracy: One of the primary benefits of using PD circulate meters is the high accuracy they provide, the high accuracy of the inner elements means preserving the clearances between the sealing surfaces to a minimal. The smaller these clearances are, the higher the accuracy associated with them. Only fluids that may bypass this seal usually are not accounted for, this is known as “bypass” or “sloshing”.
Range and repeatability: Another profit is that move meters can deal with a variety of viscosities, and it is not uncommon to expertise greater levels of accuracy when coping with excessive viscosity fluids, simply as a result of reduction of bypasses. When contemplating and comparing flowmeter accuracy, it could be very important perceive “linearity”; i.e., the flexibility of the meter to precisely measure the complete regulation ratio, and “repeatability”, i.e., the flexibility to remain accurate over a quantity of cycles. This is one other area where PD flow meters excel, with 0.02% repeatability and zero.5% linearity being standard.
Reliability: If the proper flow meter is chosen for an software, it can be expected to operate correctly for many years. Meters are sometimes sent for repair and recalibration which were within the area for 10 and sometimes 20 years of continuous use. This reliability is due largely to the truth that the same proven technology has been in use for greater than 60 years, allowing main advances to be focused on tribology and achieving the required accuracy at a reasonable price.
Low upkeep: The recommended upkeep degree is strongly influenced by the applying. For instance, if the circulate meter is dealing with a fluid with lubricating properties (i.e. oil), routine upkeep could be nearly eliminated. However, if the fluid has poor lubrication properties, then it is best to debate maintenance requirements with your distributor.
It could be very uncommon that any upkeep on a optimistic displacement move meter is more frequent than other gear inside the similar system and can be scheduled on the similar time, thus minimizing downtime.
Types of displacement circulate meters
The operation of a volumetric (PD) circulate meter consists of separating the liquid into exactly measured increments and continuing to maneuver. Each phase is counted by a connection register. Because every increment represents a discrete quantity, constructive displacement models are well-liked in automated batching and accounting applications. Volumetric circulate meters are perfect for measuring the flow of viscous liquids or the place a easy mechanical instrumentation system is required.
Positive displacement flow meters for liquids or chapter-action disc meters
Chapter-action disc meters are the most common kind of PD meter. They are used as residential water meters all over the world. As water flows through the metering chamber, it causes the disc to oscillate (chapter motion), which turns the spindle, which rotates the magnet. This magnet is coupled to a mechanical register or pulse transmitter. Because the meter captures a fixed amount of fluid each time the spindle rotates, the circulate price is proportional to the velocity of rotation of the spindle.
Oscillating piston flowmeter
Oscillating piston circulate meters are typically utilized in viscous fluid companies, corresponding to oil metering on engine take a look at stands, the place the regulation ratio is not important. These meters are additionally utilized in residential water service and might cross a restricted amount of dirt, similar to pipe scale and fantastic sand (i.e. -200 mesh or -74 micron), but not massive particles or abrasive solids.
Elliptical Gear and Convex Angle Gauges
The elliptical gear partial discharge meter makes use of two fine-tooth gears, one mounted horizontally and the opposite vertically, with the gears meshing on the tip of the vertical gear and the center of the horizontal gear. The two rotors rotate relative to every other, thereby creating interception in the crescent-shaped gap between the housing and the gears. These gauges could be very correct if the slippage between the housing and gear is stored small. If the method fluid viscosity is bigger than 10 centipoise and the move fee is greater than 20% of rated capability, an accuracy of 0.1% AR could be obtained. At lower flow charges and decrease viscosities, slippage increases and accuracy decreases to zero.5% AR or much less.
Helical meter
The Helical Meter is a volumetric system that uses two radially inclined helical gears to constantly trap the process fluid as it flows. The flow forces the helical gears to rotate within the plane of the pipe. Optical or magnetic sensors are used to encode a sequence of pulses proportional to the rotation pace of the helical gears. The drive required to rotate the helix is comparatively low, leading to a relatively low stress drop in comparability with other PD devices. The best achievable accuracy is approximately ±0.2% or price.
Metering Pumps
Metering pumps are PD devices that additionally switch kinetic energy to the process fluid. There are three primary designs: peristaltic, piston and diaphragm.
Peristaltic pumps run by systematically squeezing plastic tubing through a finger or cam right into a housing, which is also used to position the tubing. These metering pumps are utilized in laboratories, varied medical applications, most environmental sampling techniques, and for dishing out hypochlorite options. The tubing could be silicone rubber or, if a more corrosion resistant material is required, PTFE tubing can be utilized.
The piston pump delivers a fixed quantity of fluid on each “out” stroke and a hard and fast quantity of fluid into the chamber on each “in” stroke. A verify valve prevents fluid from flowing backwards. As with all positive displacement pumps, piston pumps generate pulsating move. To minimize pulsation, a number of pistons or pulsation dampening vessels are put in. Because of the tight tolerances of the piston and cylinder liner, a flushing mechanism should be supplied in abrasive functions. The size of the piston pump is dependent upon the piston displacement in addition to the required circulate and discharge stress. Select a check valve (or in critical applications, a double check valve) to stop backflow.
Diaphragm metering pumps are the most typical industrial PD pumps. A typical configuration includes a diaphragm, a chamber, and suction and discharge check valves to stop backflow. The piston may be connected directly to the diaphragm or can force hydraulic fluid to actuate the diaphragm. Maximum output strain is approximately 125 psig. variants embrace bellows diaphragms, hydraulically actuated double diaphragms, and pneumatically reciprocating double diaphragms.
Gas positive displacement flow meters
PD fuel flow meters operate by calculating the cut-off quantity of the fuel passing by way of, just like the way in which PD flow meters operate on liquids. The main difference is that the gasoline is compressible.
Diaphragm gasoline meters are mostly used to measure the flow of natural fuel, especially for household metered consumption. The meter is made of solid aluminum with a cloth-backed rubber diaphragm. The meter consists of 4 chambers: two diaphragm chambers on the inlet and outlet side and an inlet and outlet chamber in the meter physique. The passage of the gasoline via the meter creates a pressure distinction between the two diaphragm chambers via the diaphragm chamber on the compression inlet aspect and the diaphragm chamber on the expansion outlet side. This motion alternately empties and fills the 4 chambers. A slide valve at the high of the instrument alternately acts on the chambers and synchronizes the action of the diaphragms, as properly as the crank mechanism that operates the instrument register.
High Precision Positive Displacement Systems
A excessive accuracy gasoline meter is often a hybrid that mixes a regular constructive displacement meter with a motor drive that eliminates stress drop throughout the meter. Balancing inlet and outlet pressures eliminates slip, leakage and gas fugitive. In a high-precision gas meter installation, a high-sensitivity vane is used to detect differential pressure and a displacement sensor is used to measure vane deflection.
How to use volumetric flow meters?
Positive displacement flow meters measure the volumetric circulate of fluids in pipelines, similar to water, hydrocarbons, cryogenic liquids and chemical substances. Some designs can measure gasoline move, although liquid flow purposes are extra common. In liquid service, increasing viscosity reduces slip and increases the pressure drop by way of the flowmeter. Surprisingly, underneath low circulate conditions for a given volumetric circulate meter, accuracy can really improve when viscosity increases and slip decreases.
Larger strain drops across the circulate meter can prematurely wear and/or damage bearings and/or seals. Therefore, most constructive displacement circulate meters have a maximum pressure drop specification designed to limit optimistic displacement move meter bearing wear to an affordable level. Operating the meter above the meter pressure drop limit can end result in premature bearing wear and catastrophic meter failure. Note that the flowmeter size may be elevated to reduce back the stress drop in these applications. This may considerably enhance the cost, but failure to comply with this specification could also be more expensive in some purposes.
Be cautious, as broken sealing surfaces can improve slippage and scale back measurement accuracy. Using a optimistic displacement flowmeter in abrasive or dirty fluids can cause maintenance problems due to the potential for damage to sealing surfaces, damage to bearings, and/or clogging of the flowmeter. A filter could additionally be required to take away filth.
When utilizing a volumetric flowmeter, ensure that air bubbles are removed from the fluid stream. Flow measurements made in the presence of air bubbles shall be higher than the true liquid circulate because the bubble volumes are measured as in the event that they have been a certain volume of liquid. Therefore, the presence of air bubbles and (especially) the presence of varying amounts of air bubbles can adversely affect the circulate measurement related to a volumetric flow meter. Gas eliminators could also be required to take away air bubbles and mitigate this downside.
The flowmeter can be utilized for clear, sanitary, corrosive liquids similar to water and meals, in addition to some gases. Materials of development are important as a end result of small amounts of corrosion or put on can damage sealing surfaces and adversely have an result on measurement accuracy. In addition, all wetted components ought to be thought-about, including the valve physique, rotating parts, bearings and gaskets.
Municipal water districts use many volumetric circulate meters to measure residential water usage. Considering the put in base of hundreds of thousands of homes and flats with metered water service, this utility most likely represents one of many largest numbers of volumetric flowmeter purposes worldwide.
Corrosive liquid purposes are widespread in chemical industrial processes and chemical feed systems used in most industries. However, different flowmeter applied sciences could also be more suitable for these services.
Industries used
Oil and gas
Water and Wastewater
Chemical
Power
Pharmaceuticals
Food and Beverage
Pulp and Paper
Metals and Mining
Aerospace
Application concerns for volumetric move meters
Avoid utilizing Positive displacement flowmeters in dirty fluids unless fouling may be successfully eliminated upstream of the flowmeter. Operating these flowmeters in dirty fluids can lead to clogging and elevated maintenance prices. Be careful when choosing bearings, because the non-lubricated nature of sure fluids, impurities and dust can increase bearing put on and maintenance prices. Note that bearings usually don’t always fail catastrophically; they could slow down and adversely have an result on accuracy earlier than they stop working.
Avoid utilizing fluids with air bubbles until they are often effectively eliminated. As viscosity increases, make sure that the stress drop through the meter is acceptable. Make certain the viscosity of the working fluid is much like the viscosity of the calibration fluid, as totally different fluids exhibit totally different amounts of slip that can lead to measurement errors.
More articles on circulate meters:
Working principle of rotameter
Ultrasonic flow meter working principle
What is doppler move meter?
Relation between move and straine
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What is optimistic displacement circulate meter?
Positive displacement (PD) circulate meters are flow meters that provide high accuracy (±0.1% of actual circulate in some cases) and good repeatability (up to zero.05% of reading). These meters require no power supply to operate and no direct upstream or downstream piping for set up. They are properly suited to flow measurement of viscous fluids, corresponding to oils, fuels and solvents, that are difficult to measure with different forms of circulate meters.
PD flow meters are most widely utilized in residence water meters, with tens of millions of those units produced each year. Volumetric move meters can be utilized for clear, sanitary and corrosive fluids such as water and food, in addition to some gases. They are sometimes most relevant when high accuracy at an affordable worth is required.
How does a constructive displacement move meter work?
Positive displacement move meter expertise is the one flow measurement technology that immediately measures the amount of fluid passing via the meter. Volumetric flowmeters do this by repeatedly intercepting fluid to measure its flow rate. This course of can be regarded as repeatedly filling a bucket with fluid before pouring the contents downstream. The variety of times the bucket is filled and emptied signifies the flow rate by way of the flowmeter. There are many volumetric flow meter geometries available.
Retention is typically achieved using rotating components that kind a transferring seal between one another and/or the flowmeter physique. In most designs, the rotating components have tight tolerances so that these seals stop fluid from passing by way of the flowmeter with out being measured (sloshing). In some volumetric flowmeter designs, bearings are used to assist the rotating parts. Rotation can be sensed mechanically or by detecting the motion of the rotating components. As extra fluid flows, the rotating components rotate proportionally faster. The transmitter processes the signal generated by the rotation to determine the move price of the fluid. Some volumetric circulate meters have mechanical registers that present the total flow fee on an area show.
Features
Suitable for smaller line sizes, low move rates, excessive viscosities and long durations, particularly for oils. The disadvantages are that there are shifting elements to put on, maintenance required, more impurities, and never as up to date as other technologies with new protocols, and so forth.
Accuracy: One of the primary advantages of using PD flow meters is the high accuracy they offer, the high accuracy of the inner components means maintaining the clearances between the sealing surfaces to a minimal. The smaller these clearances are, the upper the accuracy related to them. Only fluids that can bypass this seal usually are not accounted for, this is called “bypass” or “sloshing”.
Range and repeatability: Another benefit is that move meters can deal with a variety of viscosities, and it isn’t uncommon to expertise larger levels of accuracy when coping with excessive viscosity fluids, merely due to the reduction of bypasses. When considering and comparing flowmeter accuracy, you will need to perceive “linearity”; i.e., the power of the meter to accurately measure the complete regulation ratio, and “repeatability”, i.e., the power to remain correct over a number of cycles. This is one other space the place PD circulate meters excel, with zero.02% repeatability and 0.5% linearity being standard.
Reliability: If the right flow meter is selected for an software, it may be anticipated to operate correctly for many years. Meters are often sent for restore and recalibration which have been in the field for 10 and typically 20 years of continuous use. This reliability is due in giant part to the truth that the same confirmed technology has been in use for greater than 60 years, allowing major advances to be focused on tribology and attaining the required accuracy at an inexpensive price.
Low maintenance: The recommended maintenance stage is strongly influenced by the appliance. For instance, if the circulate meter is dealing with a fluid with lubricating properties (i.e. oil), routine upkeep may be nearly eradicated. However, if the fluid has poor lubrication properties, then it’s best to discuss upkeep requirements together with your distributor.
It may be very rare that any upkeep on a constructive displacement circulate meter is more frequent than different equipment within the same system and may be scheduled at the identical time, thus minimizing downtime.
Types of displacement flow meters
The operation of a volumetric (PD) move meter consists of separating the liquid into exactly measured increments and persevering with to move. Each segment is counted by a connection register. Because every increment represents a discrete volume, positive displacement models are well-liked in automated batching and accounting applications. Volumetric circulate meters are good for measuring the move of viscous liquids or where a simple mechanical instrumentation system is required.
Positive displacement flow meters for liquids or chapter-action disc meters
Chapter-action disc meters are the most typical sort of PD meter. They are used as residential water meters around the globe. As water flows through the metering chamber, it causes the disc to oscillate (chapter motion), which turns the spindle, which rotates the magnet. This magnet is coupled to a mechanical register or pulse transmitter. Because the meter captures a fixed quantity of fluid every time the spindle rotates, the circulate fee is proportional to the pace of rotation of the spindle.
Oscillating piston flowmeter
Oscillating piston circulate meters are sometimes utilized in viscous fluid services, corresponding to oil metering on engine test stands, where the regulation ratio isn’t critical. These meters are additionally used in residential water service and may cross a limited amount of dust, corresponding to pipe scale and fine sand (i.e. -200 mesh or -74 micron), however not massive particles or abrasive solids.
Elliptical Gear and Convex Angle Gauges
The elliptical gear partial discharge meter uses two fine-tooth gears, one mounted horizontally and the other vertically, with the gears meshing on the tip of the vertical gear and the middle of the horizontal gear. The two rotors rotate relative to each other, thereby creating interception within the crescent-shaped gap between the housing and the gears. These gauges can be very correct if the slippage between the housing and equipment is saved small. If the method fluid viscosity is bigger than 10 centipoise and the circulate fee is larger than 20% of rated capacity, an accuracy of 0.1% AR may be obtained. At lower circulate charges and decrease viscosities, slippage will increase and accuracy decreases to zero.5% AR or less.
Helical meter
The Helical Meter is a volumetric gadget that uses two radially inclined helical gears to continuously entice the process fluid as it flows. The move forces the helical gears to rotate in the airplane of the pipe. Optical or magnetic sensors are used to encode a sequence of pulses proportional to the rotation pace of the helical gears. The drive required to rotate the helix is comparatively low, leading to a relatively low stress drop in comparability with other PD devices. The best achievable accuracy is roughly ±0.2% or rate.
Metering Pumps
Metering pumps are PD devices that also transfer kinetic vitality to the method fluid. There are three basic designs: peristaltic, piston and diaphragm.
Peristaltic pumps run by systematically squeezing plastic tubing through a finger or cam into a housing, which is also used to place the tubing. These metering pumps are used in laboratories, various medical functions, most environmental sampling techniques, and for dishing out hypochlorite solutions. The tubing can be silicone rubber or, if a extra corrosion resistant materials is required, PTFE tubing can be utilized.
The piston pump delivers a onerous and fast quantity of fluid on every “out” stroke and a set quantity of fluid into the chamber on every “in” stroke. A examine valve prevents fluid from flowing backwards. As with all constructive displacement pumps, piston pumps generate pulsating circulate. To minimize pulsation, multiple pistons or pulsation dampening vessels are installed. Because of the tight tolerances of the piston and cylinder liner, a flushing mechanism should be supplied in abrasive applications. The dimension of the piston pump is decided by the piston displacement in addition to the required circulate and discharge pressure. Select a examine valve (or in important applications, a double verify valve) to stop backflow.
Diaphragm metering pumps are the most typical industrial PD pumps. A typical configuration features a diaphragm, a chamber, and suction and discharge check valves to forestall backflow. The piston may be connected directly to the diaphragm or can pressure hydraulic fluid to actuate the diaphragm. Maximum output pressure is approximately 125 psig. variants include bellows diaphragms, hydraulically actuated double diaphragms, and pneumatically reciprocating double diaphragms.
Gas constructive displacement circulate meters
PD gasoline move meters function by calculating the cut-off quantity of the fuel passing via, just like the way in which PD circulate meters operate on liquids. The main distinction is that the gasoline is compressible.
Diaphragm fuel meters are mostly used to measure the circulate of pure gasoline, especially for household metered consumption. The meter is made from cast aluminum with a cloth-backed rubber diaphragm. The meter consists of four chambers: two diaphragm chambers on the inlet and outlet facet and an inlet and outlet chamber within the meter body. The passage of the gas via the meter creates a strain distinction between the two diaphragm chambers by way of the diaphragm chamber on the compression inlet side and the diaphragm chamber on the expansion outlet side. This action alternately empties and fills the four chambers. A slide valve at the high of the instrument alternately acts on the chambers and synchronizes the motion of the diaphragms, in addition to the crank mechanism that operates the instrument register.
High Precision Positive Displacement Systems
A excessive accuracy fuel meter is typically a hybrid that mixes a regular positive displacement meter with a motor drive that eliminates stress drop throughout the meter. Balancing inlet and outlet pressures eliminates slip, leakage and gas fugitive. In a high-precision gas meter installation, a high-sensitivity vane is used to detect differential pressure and a displacement sensor is used to measure vane deflection.
How to make use of volumetric move meters?
Positive displacement flow meters measure the volumetric flow of fluids in pipelines, corresponding to water, hydrocarbons, cryogenic liquids and chemicals. Some designs can measure gas move, though liquid flow purposes are more widespread. In liquid service, increasing viscosity reduces slip and will increase the stress drop via the flowmeter. Surprisingly, beneath low flow circumstances for a given volumetric flow meter, accuracy can really improve when viscosity will increase and slip decreases.
Larger pressure drops throughout the move meter can prematurely wear and/or harm bearings and/or seals. Therefore, most constructive displacement flow meters have a most strain drop specification designed to limit optimistic displacement circulate meter bearing wear to an inexpensive degree. Operating the meter above the meter pressure drop restrict may find yourself in premature bearing wear and catastrophic meter failure. Note that the flowmeter measurement can be increased to reduce the pressure drop in these purposes. This may considerably enhance the fee, but failure to comply with this specification may be more expensive in some purposes.
Be cautious, as damaged sealing surfaces can increase slippage and scale back measurement accuracy. Using a positive displacement flowmeter in abrasive or dirty fluids may cause upkeep problems due to the potential for injury to sealing surfaces, harm to bearings, and/or clogging of the flowmeter. A filter may be required to remove filth.
When using pressure gauge ลม , be certain that air bubbles are removed from the fluid stream. Flow measurements made in the presence of air bubbles might be higher than the true liquid flow as a result of the bubble volumes are measured as in the event that they had been a sure quantity of liquid. Therefore, the presence of air bubbles and (especially) the presence of varying amounts of air bubbles can adversely affect the flow measurement related to a volumetric move meter. Gas eliminators may be required to remove air bubbles and mitigate this problem.
The flowmeter can be utilized for clear, sanitary, corrosive liquids such as water and meals, in addition to some gases. Materials of development are necessary because small amounts of corrosion or wear can damage sealing surfaces and adversely have an result on measurement accuracy. In addition, all wetted components must be thought-about, including the valve physique, rotating components, bearings and gaskets.
Municipal water districts use many volumetric circulate meters to measure residential water usage. Considering the put in base of hundreds of thousands of houses and apartments with metered water service, this application most likely represents one of the largest numbers of volumetric flowmeter purposes worldwide.
Corrosive liquid applications are common in chemical industrial processes and chemical feed systems used in most industries. However, other flowmeter technologies could additionally be more suitable for these services.
Industries used
Oil and fuel
Water and Wastewater
Chemical
Power
Pharmaceuticals
Food and Beverage
Pulp and Paper
Metals and Mining
Aerospace
Application concerns for volumetric circulate meters
Avoid using Positive displacement flowmeters in dirty fluids unless fouling could be successfully eliminated upstream of the flowmeter. Operating these flowmeters in soiled fluids can lead to clogging and elevated upkeep costs. Be careful when deciding on bearings, as the non-lubricated nature of certain fluids, impurities and filth can improve bearing put on and maintenance costs. Note that bearings usually don’t all the time fail catastrophically; they might decelerate and adversely affect accuracy earlier than they cease working.
Avoid using fluids with air bubbles unless they can be effectively removed. As viscosity will increase, ensure that the stress drop via the meter is suitable. Make positive the viscosity of the working fluid is similar to the viscosity of the calibration fluid, as totally different fluids exhibit totally different amounts of slip that can result in measurement errors.
More articles on flow meters:
Working precept of rotameter
Ultrasonic flow meter working precept
What is doppler circulate meter?
Relation between move and straine