Single stage reciprocating air compressor pdf. Two stage versions can improve specific power up to 15% and some can achieve higher discharge pressures. Legendary Performance. Consequently, it is necessary to locate a sensitive data acquisition point for a robust fault diagnostic method. Explain the working of single stage reciprocating air compressor. In a single stage reciprocating air compressor, compression takes place in one stage while the multi-stage type involves more than one compression stage for achieving the required high pressure and low temperature by using intercooler [13]. The above figure is free to use however attribution to The Mechanical post is needed. The machine consist of two industrial compressors, one with a low pressure cylinder and other with a high pressure cylinder, an intercooler between the two stages and an air receiver. The compressors used for compressing air are called air compressors. All compressors are equipt with pressure switch, safety valve, manometer, non-return valve, condensate drain valve and air outlet valve. KNOW MORE CONNECT WITH US. Mar 11, 2023 · A reciprocating compressor has a piston that moves downwards thus reducing pressure in its cylinder by creating a vacuum. Typically, high-speed compressors run at a speed of 900 to 1200 rpm, and slow-speed units at speeds of 200 to 600 rpm. A reciprocating compressor is a positive displacement machine in that a volume of gas is drawn into a compressor cylinder’s compression chamber where it is trapped, compressed and pushed out. ) Drill Bit Size (In. of Science, Professor in Compressor Engineering V. The belt-driven pump features aluminum construction and a cast-iron sleeve. us Please include the unit serial number located on the control panel with all inquiries. Table 1 presents the specifications of the air compressor. Any automotive place will have them for sell, Home Depot and Lowe’s have them in the aisle. This formula provides an estimate of the power required under idealized conditions. Piston: Single stage air compressors have one piston, which is used for the compression of air. The document describes a multi-part assignment on reciprocating air compressors. A single-stage reciprocating piston compressor works by drawing the air into the cylinder where it is compressed in a single-piston stroke of approximately 120 PSI and then sent to a storage tank. The Sep 15, 2016 · The main difference between single- and two-stage compressors is the number of times that air gets compressed between the inlet valve and the tool nozzle. A compressor using both sides of the piston is considered as double acting. Engja [5] has developed the bond graph model of single stage reciprocating air compressor however in this study the main aim is to author the standard library for different domains. The document summarizes key concepts about reciprocating air compressors: 1) It describes the basic components and working of a single-stage, double-acting reciprocating air compressor using a labeled diagram. 5 hp and 7. LF: Single-stage two-cylinder oil-free reciprocating The Single-Stage Belt Drive Reciprocating Compressors are designed for continuous duty application. 3will assess multistage dimensioning. Single stage reciprocating air compressors are perfect for light work at home and/or in small workshops. Low capacity compressor (delivers 0. In a single-stage compressor, the air is compressed one time; in a two-stage compressor, the air is compressed twice for double the pressure. Apr 18, 2019 · This paper presents the performance assessment of a two-stage reciprocating air compressor operating at an Oil and Gas Terminal in Rivers State, Nigeria. The intake gas enters the suction manifold, then flows into the compression The reciprocating air compressor is single acting when the compressor is accomplished using only one side of the piston. The pressure in the system will start to build and stabilize over time. It also provides numerical problems to calculate values like mean effective pressure, power These paper mainly focus on the positive displacement compressor and that of the sub part is reciprocating gas compressor and their design, modelling, analysis and development i. Fig. 10 Intercooling 13. For those who need a little more power, our single & two-stage, splash lubricated . The following are the specifications of the double acting reciprocating air compressor: The unit consists of a two stage reciprocating air compressor with second stage connected via a finned type air cooled intercooler to the first stage as well as after cooler has been made effective by providing a fan blade type of pulley. Material and methods The machine that was used is a GT103 two-stage compressor test set. 7 Volumetric Efficiency of Reciprocating Compressors 13. A reciprocating, 2-stage, single acting air compressor has a rated capacity of 0. When performance is defined by maximum operating pressure, increased air flow and extended duty cycles, Ingersoll Rand is the product of choice. 4mm (29. (i) Single stage compressor, for delivery pressure up to 5 bar (ii) Two stage compressor, for delivery pressure between 5 and 35 bar (iii) Three stage compressor, for delivery pressure between 35 and 85 bar ELGi’s two stage high volume compressor is meticulously designed with cutting-edge technology proven around the world. Drill 2-1/4” deep holes using a concrete drill bit sized per the following table. Depending on your application, the following accessories may be required: l An air pressure regulator to adjust the air pressure entering the tool or accessory. The size of cylinder is very large when compared to the cylinders in the multistage compressor. 15, fluid medium - Gas. Apr 23, 2016 · 31. ) KPCL Reciprocating, Horizontal Balanced Opposed and Piston Compressors are the results of extensive engineering expertise and experience of over five decades in design, manufacturing, supply and installation of air and gas compressors of various designs, capacities and pressures for a range of applications. Easy to Service: Individually cast cylinders, overhung crankshaft and one piece connecting rod simplifies maintenance and Designed for any environment, our 3 and 5 hp single stage compressors are ideal for almost anyone, from individuals that thrive on do-it-yourself projects to the professional air compressor user. Two-Stage Reciprocating Air Compressors. 7” Hg) for two stage configuration, at sea level. Multi stage air compressor is used in places where high pressure air is required. ELGi reciprocating air compressors are designed for optimum efficiency while requiring minimum maintenance to meet your demands of compressed air. 60 29. there is cylinder, piston, connecting rod, crankshaft and suction and discharge valves etc as shown in . View and Download Ingersoll-Rand 2545 owner's manual online. These pumps achieve vacuum upto 737mm (29. Page 1 TS Series TS05 to TS15 Two-Stage Reciprocating Air Compressor OPERATION AND MAINTENANCE MANUAL Page 2 FAX: 704-944-8338 www. 1 Construction. ethylene glycol. Multi-stage reciprocating compressor. Rotary screw vacuum pumps are available from 80 to 3,000 cfm delivering vacuum levels to 29. 2545 air compressor pdf manual download. It is different from double and multiple stage air compressors crankshaft. (204 KPa) 38. The Reciprocating Air Compressor accomplishes this by a piston within a cylinder as the compressing and displac-ing element specified as single or double-stage and single or double-acting. Diaphragm reciprocating compressor. Fig 4: Single Stage Reciprocating Air Compressor Schematic. You see them everywhere. P cylinders) are driven by a single prime mover through a common shaft. Single-stage compressors use a single piston stroke to fill the cylinder compressors, based on a cylinder and a piston, results in being intuitive [19], so a reciprocating compressor will be considered. Parameters in the system can be recorded through pressure – and temperature gauges set up at the piston, after cooler, receiver and nozzle discharge. This document provides information on single and two-stage industrial reciprocating air compressors made by ELGi. The single and multi-stage reciprocating Single Stage Electric Driven Reciprocating Air Compressor 3-5 hp. QUICK REFERENCE Recommended Oil (2 Options) FSC-1000A ISO-100 Premium Reciprocating Compressor Lubricant Compressor is a device which is. This is a splash lubricated single stage air compressor system A single-stage reciprocating compressor is a type of compressor in which the gas or air is compressed in a single stage. E. air), Medium capacity compressor (delivers 5 cubic meter /s of compressed air) and. 5 Efficiency of a Compressor 13. Home air compressors often use single-stage, while compressors in businesses or industries are often two-stage. It is an object of the present invention to provide an improved reciprocating compressor which may be utilized for compressing air and other gases, such as, for example, air conditioning, heat pumps, pneumatic compression, and for various other gas compression purposes. Thermal overload protected motors are standard on 1/2 through 1 HP, single phase, 115 Volt units. 1 shows the AutoCAD 3D Model of the single-acting reciprocating Two-Stage vs. Apr 16, 2024 · Air and Gas Compressors Question 4: A single - stage, reciprocating air compressor takes in 1. e. continuous duty operation with the use of petroleum lubricant. The thermodynamic cycle of an ideal air compressor consists of four states and is illustrated in Figure 1. Most single stage units will work happily for years if you don't use them too much, for example in a one-man workshop. Whether for vehicle services, commercial or industrial applications, we will assess and propose the most cost-effective solution that increases the productivity of your installation. Easy-access valve pockets. 00 2. Any other use of these units will void the warranty and the manufacturer will not be responsible for problems or damages resulting from such misuse. High-pressure cast-iron pistons for maximum durability. 6 Single Stage, Single Cylinder, Reciprocating Air Compressor. Whether it's powering pneumatic tools, operating These two-stage compressors can operate at 1-25 horsepower (hp) and are 100% duty cycle-rated for maximum operational safety. It is designed to house one cylinder that compresses air with a single piston stroke. 4. two stage reciprocating air compressor by providing water cooling source, radiator coolant and. 5 hp model that can deliver 12. A two-stage compressor includes an additional step where the air is compressed by a second, smaller piston to a pressure of up to 175 PSI. IJE RT P. The main focus was to investigate the 47732397001 - For 4-footed horizontal tank Kohler diesel engine driven compressors To mount the compressor to a concrete surface, use the following procedure: Mark the location of the mounting holes. 6 Work of Compression - Reciprocating Compressors 13. 2 m 3 /kg. Individual cylinders are small when compared to single cylinder compression. Single-acting, reciprocating air compressors are generally air-cooled. The paper provides much needed information regarding the efficiency of the compressors operating under the same conditions with the same system parameters. Easy access to the pump components in our reciprocating compressors allows for routine maintenance and replacement of parts like The single-stage direct-drive reciprocating piston air compressor provides better oil control and cooling, low noise, easy mobility, and easy maintenance, which helps save power. The P-V diagram is a plot of the pressure of the gas versus the volume of the gas trapped in the compression chamber. Reciprocating Air Compressors. The single stage air compressor has one cylinder that contains the gas that is to be compressed. l An air line filter for removal of moisture and oil vapor in compressed air. The experiments of a two double-cylinder reciprocating compressor system with air, water and different inter coolants were performed. Centrifugal: Operate by accelerating the air. Summary of Contents for ELGi TS Series. Go through the capacity control diagram given for We are manufacturing following 9 types of Two Reciprocating Compressor 5. Figure 1. This paper also reports on investigation carried out on the effect of pressure Question: 1. The crankshaft is driven by a turbine/ engine/ electric motor. A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure. The compressor used in this experiment is an Integersol-Rand type 30 two-stage air compressor. Explain the work done by a single stage reciprocating air compressor 3. 2. 13. For over 100 years, our reciprocating compressors have delivered rock-solid performance for the most demanding applications. 1 INTRODUCTION Compressors are work absorbing devices which are used for increasing pressure of fluid at the expense or work done on fluid. Ingersoll Rand has designed reciprocating single stage air compressors and two stage air compressors to last a lifetime — Thanks to quick, easy maintenance with renewable components. The discharge pressure is 30 kg/cm2 and the air is discharge into an air receiver of 1250 Liters capacity. 05-25 HP reciprocating air compressor is the way to go. And with an extensive service network and easy availability of spares, this compressor is undoubtedly the wisest choice for unparalleled performance in the long run. Ingersoll Rand single- and two-stage reciprocating air compressors are an ideal choice for applications that demand a reliable air supply for everyday use. OPERATING INSTRUCTION AND a) Compressor model used CAPACITY CONTROL SYSTEM TWO STAGE b) Gas used in Refrigeration system COMPRESSOR c) Design condensing saturation temp. Artificially cooled, pressure ratio more than 1. P) cylinder. [1] [2] Pressures of up to 5,000 PSIG are commonly produced by multistage reciprocating compressors. So, the double-acting air compressor has four valves (2 outlets and 2 inlet valves), as shown in the above-given diagram. P) cylinder, an intercooler and a high pressure (H. It describes the key features and benefits of ELGi compressors, including their reliability, cost effectiveness, energy efficiency, and focus on operator safety. Ingersoll Rand single- and two-stage reciprocating compressors offer you more performance and feature choices. Tank Size (Gal. These single-stage cylinder belt driven reciprocating compressors are reliable workhorses and can generate up to 10 bar g pressure suitable for most of the industries and automotive applications. PRESSURE - VOLUME DIAGRAM. Scherba, Candidate of Sc1ence A. Model Piston Displacement Vacuum (Hg) Motor cfm inch hp V235 21. This difference in pressure forces the suction chamber valves to open and bring gas or air in. Jul 6, 2022 · Two-stage reciprocating air compressor: this is a type of reciprocating air compressor that compresses air in two stages and in between the stages the air is cooled. The internal energy of the air leaving is 100 kJ/kg greater than the air entering. air and forcing it into a smaller volume. Single-Stage. In diaphragm compressor type (also known as a membrane compressor) the compression of gas occurs by the movement of a flexible membrane instead of an Electric-Driven Single Stage – Air Cooled Our Single-Stage electric air compressors are ideal for most professional compressor user. The reciprocating piston air compressors from ELGi are suitable for spray painting, fabrication workshops, pneumatic tools, etc. 11 Minimum Work in TWO Stage Compression with Intercooling Dec 14, 2015 · Also this investigation is concerned with the improving efficiency of. Download Solution PDF. Also for: 2475, 2340, 7100, 15t, 3000, 2475n5-v, 2545k10-v, 2545e10-v, Value plus 2545k10-vp, Value plus 2545e10-vp. The Quincy QR-25 has many key features, including: Intake unloaders for loadless starting, increased energy savings and reduced motor wear. I. 7 in Hg. 0” Hg) for single stage and upto 754. According to Capacity. Our compressor range is known for its Your air compressor unit is suitable for operating air tools, caulking guns, grease guns, sandblasters, etc. Your choices include single-stage or two-stage compressors, gas engine or electric motors, portable or stationary models and specifi c accessory packages that best match your application. Air pressure ratings are available up to 125 PSIG. The efficiency is typically expressed as a decimal between 0 and 1. d) Design saturation evaporation temp. The compressor consists of a piston that reciprocates in a cylinder driven by a crankshaft, with inlet and outlet Reciprocating air compressors may be single or double acting, single stage or multi-stage [11], [12]. After the engine is running for a sufficient time (approx. Cabakow, cand1date of Sc1ence THESIS At the present t1me one of the main ways to PROCEDURE. Figure 1: Ideal Thermodynamic Cycle of an Air Compressor Figure 1 can be described as follows: • 1-2: Isentropic Compression of Air • 2-3: Air delivery at constant pressure and temperature • 3-4: Isentropic Expansion of Air 6 single stage and two stage designs are available, with two stage designs beginning at 125 hp. P and H. pdf), Text File (. 4 kg of air per minute at 1 bar and 17°C and delivers it at 6 bar. SINGLE-STAGE POSITION DISPLACEMENT COMPRESSOR WORK PROCESSES WITH A TWO-PHASE WORKING MEDIUM P. Oil-lubricated high-pressure reciprocating compressors, up to 500 bar (a) (7250 psia), 37-165 kW: B&D 45 Oil-lubricated high pressure trunk-piston compressors, up to 351 bar(a) 5090 psia), 22-200 kW: CU/CT/CN 46 Oil-lubricated gas screw compressors, 16 bar(a) (232 psia): GG-VSD 47 Car and bus refueling stations: S100/S750 48 Nov 17, 2019 · Single-Stage vs Multi-Stage Reciprocating Compressor Depending on the speed, Reciprocating compressors are classified as either high speed or slow speed. Some dual-acting cylinders in high-pressure applications will have a piston rod on both Your air compressor unit is suitable for operating air tools, caulking guns, grease guns, sandblasters, etc. From these survey we also find the whole process of reciprocating gas compressor and there future Turn on the power switch and ammeter, where compressed air would start circulating in the system (pressurising tank). General Description. 02 m3/sec of free air at 101 KPa and 27 C when running at 600RPM. pdf. So, the overall formula for the power required to drive a single-stage reciprocating compressor becomes: P = P 1 ⋅ V 1 ⋅ln ( V 2 /V1) /n. Climate Control. This cylinder is connected to a power supply that provides the force needed to compress the air. single-or dual-acting design. (1) Simplex, two stage air compressor process. The process within a two-stage compressor is sure. 95 is obtained from the Atlas Copco data sheet. We stated in the last post that reciprocating compressors are positive displacement compressors that use a Ingersoll Rand single- and two-stage reciprocating compressors offer you more performance and feature choices. August 25, 2017. 5. The compression follows the law PV 1. The basic construction is similar to as that of an IC engine i. 5 hp compressor models include starting switch and the working principle of these compressors is as start-stop. Unloading has been provided by the automatic drain on pressure switch. Let us refer to the image below as we learn more about the type. Single-stage: When the entire compression is accomplished with a single cylinder or a group of cylinders in parallel gen-erally used for pressures in A reciprocating compressor is a positive displacement machine in that a volume of gas is drawn into a compressor cylinder’s compression chamber where it is trapped, compressed and pushed out. When performance is defined by maximum operating pressure, increased air flow and Ingersoll Rand single- and two-stage reciprocating compressors offer you more performance and feature choices. 0 Show all. The Quincy single stage reciprocating air compressor lineup includes: Q13160VQ: This Quincy 60-gallon air compressor is a stationary 3. Reciprocating compressors are commonly called piston compressors. Sep 7, 2023 · A single-stage reciprocating air compressor is employed in this present study. Single stage air compressor’s piston moves upward and backward in the cylinder to compress the air. It is simple to operate and easy to maintain. If you define unsurpassed performance by maximum operating pressure, increased air flow and extended duty cycles, you can count on an Ingersoll Rand reciprocating air compressor to deliver it reliably. 6. And also, the air is compressed only one time. Single stage 5. used to increase the pressure and converting the energy to pressure of air from low pressure to high. ELGI COMPRESSOR An experimental test rig has been built to test reciprocating compressors of different size and capacity. The main shaft or crank shaft is rotated by some external prime over i. The most common air compressor in the fractional and If the compression is PVk = C, find the mean effective pressure in KPa. Simply put, a piston moves in a reciprocating manner to compress the gas. Speed (N) = 160rpm 160/6 0 The air compressor units are to be mounted per the instructions provided on a solid floor. N. The temperature of fluid due to compression is very high. . Maximum Power and Flexibility: 100% continuous duty, 5 hp 230 V two-stage air compressor, 175 psig maximum operating pressure and an 80 gallon ASME receiver tank provide plenty of punch for the most demanding applications. 35 = C. an IC engine Ingersoll Rand single- and two-stage reciprocating compressors offer you more performance and feature choices. FS Curtis manufactures a broad array of compressor configurations to satisfy the needs of our diverse customer base. Reciprocating air compressors can be classified into single-acting and double-acting reciprocating air compressors. Problem Overview Ingersoll Rand single- and two-stage reciprocating compressors offer you more performance and feature choices. 2will illustrate how the flow and compression requirements might not be met with single stage compression; Section5. The single-stage series of Commandair air compressor packages are available from 1/2 through 3 HP, with the option of horizontal or vertical style receivers, or as base mounted. Air flows steadily at the rate of 1 kg/s through an air compressor at 10 m/s, 100 kPa and 1 m 3 /kg and leaving at 6 m/s, 800 kPa and 0. This paper focuses on the single-acting reciprocating compressor where the air that is compressed in the cylinder is on one side of the piston only. Each air compressor features durable cast-iron construction, 100% continuous duty cycle for the toughest applications and extended pump life for years of trouble-free service. High capacity compressor (delivers more than 5 cubic meter /s of compressed air). The body of this compressor sets according to the arrangement of the piston and cylinder. Jan 3, 2024 · Single Acting Reciprocating Air Compressors. Core values that benefits the customer. Piston speed (2lN) = 150m /min. This compressor uses a single cylinder and a piston for the compression of air. shows the general arrangement of a two-stage air compressor. Elgi reserves the right to make changes and improvements to update products All of these requirements are met by the Ingersoll Rand T30 air cooled reciprocating single stage and two Stage vacuum pumps. 8 cfm at 90 psi and 14. 8 Volumetric Efficiency and Clearance 13. The two-stage reciprocating air compressor provides higher pressure and is characterised by lower discharge temperature (140 0 C to 160 0 C) compared to the single-stage which has 5. 1 GENERAL 2. Reciprocating piston air compressors use pistons to pressurize the air in a cylinder using either a single- or two-stage process. elgi. Oct 18, 2021 · Types of reciprocating compressor. Power (P) = 150KW. Single-stage reciprocating compressor. with the use of Ingersoll Rand svnthetic compressor lubricant and 60% Close the service valve fully. Apr 6, 2022 · compressor notes. The double-acting reciprocating compressor working principle is very simple. Because the compressed air temperature out of the compressor is 10°C higher than the ambient tempera- ture, the refrigerant dryer inlet temperature will be maximum 30 + 10 = 40°C. Both the pistons (in L. 31. LZ: Automatically or Elektronikon® Mk5-controlled single-stage oil-free reciprocating compressor, silenced, with a maximum working pressure of 10 bar (145 psi). Show transcribed image text. But if you require more air (two-man workshop) or use a lot of power tools (compressed air powered grinders, drills, etc (b) Based on number of stages: Compressors can be single stage or multistage. In this type, one end of the piston is used for suction and compression. Apr 16, 2024 · Reciprocating Compressors Question 4: A single - stage, reciprocating air compressor takes in 1. RELEASED 05/Apr/2018 15:16:08 GMT OPERATION GENERAL WHEN YOU ARE FINISHED: Your air compressor was designed for 100% continuous duty operation Set the pressure switch lever to ‘OFF”. Air is drawn into the compressor through the air intake and filter assembly. When the cylinder goes up, it increases pressure thus forcing the gas or air out of the cylinder through a discharge chamber . [4] have demonstrated complete Bond graph of engine cooling system, which is taken further for developing intercooler of the air compressor H. Intercooler pressure drop (P3 - P2). This compressor delivers high air flow rates and high operating pressures, making it perfect for demanding tasks. Robust, reliable and long lasting. 10 minutes), the following reading should be taken: Low pressure cylinder inlet and discharge pressures (PI and P2). The piston of each cylinder is driven by a prime mover electrical motor The following are the specifications of the double acting reciprocating air compressor: The unit consists of a two stage reciprocating air compressor with second stage connected via a finned type air cooled intercooler to the first stage as well as after cooler has been made effective by providing a fan blade type of pulley. Reciprocating compressors are mainly classified into 3 types. SUMMARY A two stage reciprocating compressor includes a casing. What are the advantages of Multistage compression. of system. Technical specifications are provided for a range of ELGi compressor models from 3 to 40 horsepower. 3. There is a fan similar to a single-acting air compressor. 35 = constant, calculate the indicated power input to the compressor. • Industrial quality design Mar 15, 2024 · Compressor Question 6. Despite this diversity, all FS Curtis two stage compressor configurations work off the same basic cycle. The best position for the accelerometer sensor to capture the vibration signals is selected. Two Stage High Volume Oil-lubricated Reciprocating Compressor. Feenstra et al. 15 cubic meter /s of compressed. This may be of. Single and Two Stage Oil-lubricated Reciprocating Compressor. These are commonly known as single stage reciprocating air compressors. Also this investigation is concerned with the improving efficiency of two stage reciprocating air compressor by providing water cooling source, radiator coolant and ethylene glycol. 3 /6. 9 Volumetric Efficiency and Pressure Ratio - Multistage Compression 13. Assuming that the compression process follows the law pV 1. When the piston moves backward, it sucks the air. A single stage double acting air compressor of 150KW power takes air in at 16 bar & delivers at 6 bar. A single stage air compressor works using the force of a piston and pressure sensitive valve. Section5. Determine the size of the cylinder. It consists of a low pressure (L. Given data . In Figure 1, P S High pressure compressors in which the final delivery pressure is 80 to 100 bar. With the aid of a diagram, explain two-stage reciprocating air compressor with intercooler 5. 6 cfm at 40 psi. the compressor runs at 160rpm with average piston speed of 150 m/min. With its splash lubrication system and rugged construction, this compressor ELGI - Free download as PDF File (. In addition, the desired pressure dew point is +5°C. It includes questions about describing the working principles, drawing diagrams, defining efficiencies, deriving equations for work, volumetric efficiency and free air delivery for single-stage and multi-stage compressors. from raw stage to the final stage of reciprocating gas compressor. Aug 25, 2017 · Compressor Basics: Reciprocating. Designed for any environment, our 3 and 5 hp single stage compressors are ideal for almost anyone, from individuals that thrive on do-it-yourself projects to the professional air compressor user. The appropriate correction factor 0. The compressors were tested with air as working fluid . Plast1n1n, Dr. These may be single- stage, usually rated at discharge pressures from 25 to 125 pounds per square inch gauge (psig), or two-stage, usually rated at discharge pressures from 125 psig to 175 psig or higher. Compressors are invariably used for all applications requiring high pressure air. LFxD: Single-stage oil-free reciprocating compressor with integrated dryers and a maximum working pressure of 10 bar (145 psi). txt) or read online for free. uq tc di jf th mv st xg rs td