Displacement Meters and PD Elements for Custody Transfer and Mechanical Billing Systems

Quick Answer: Silver Automation Instruments supplies positive displacement flow meters and PD elements for custody transfer in diesel, fuel oil, palm oil, and chemical dosing. These meters fit DN15 to DN150 lines, handle viscosities from 0.5 cP to 5000 cP, and repeat at 0.03 percent. Send your pressure in bar, temperature in °C, pipe size in DN, and flow range in liter per hour for a fixed quotation.

Most engineers skip the theory and ask one question. Will the meter keep a total when power fails? A positive displacement meter will. The rotating element captures a fixed volume per cycle. The gear train moves a mechanical counter. That counter stays on the dial even after shutdown. Because of this, PD elements still appear in remote fuel depots and small billing skids where electronic totalizers are not practical.

Why Positive Displacement Meters Work for Custody Transfer

Positive displacement meters measure volume directly. A pair of oval gears or a rotary piston divides the flow into small fixed segments. Accuracy stays stable at low flow. The turndown is often better than a turbine meter at high viscosity. For custody transfer, repeatability matters more than absolute precision. A PD meter with plus or minus 0.5 percent accuracy and 0.03 percent repeatability gives the same number every time the same volume passes. This repeatability reduces disputes between supplier and buyer.

In practice, a diesel loading rack in Indonesia can total 2000 liters per batch. A small change of 5 liters causes a billing argument. We have seen this on customer sites many times. A mechanical PD meter solves the problem because the counter is visible and does not need a flow computer. The truck driver and the plant operator read the same dial.

Mechanical Billing Systems Without Power

Mechanical billing systems still matter in Southeast Asia, Africa, and remote parts of Oceania. Many sites have no stable 24 V DC supply. Some have solar power only. A PD meter with a mechanical register needs no power for totalization. The batch knob can be reset before a delivery. The non resettable total keeps the lifetime volume. That total is the audit trail for buying and selling.

But some users need an electronic output. We add a reed switch or a 4-20 mA HART transmitter to the same meter. This gives the local mechanical total plus a remote signal. The pulse output can feed a PLC or a small billing panel. For hazardous areas, ATEX Zone 1 certification is available on the PD elements. Temperature compensation with PT100 is an option for heated oil lines.

Model Selection for Common Fluids

Silver Instruments offers oval gear flow meters for clean hydrocarbons and low viscosity chemicals. For diesel, light fuel oil, and kerosene, the OG series covers DN15 to DN80. A DN25 OG meter handles 60 to 600 liters per hour at 3 cP. A DN40 unit covers 200 to 3000 liters per hour. Accuracy stays inside plus or minus 0.5 percent of reading.

For palm oil, heavy oil, molasses, or resin from 100 cP to 5000 cP, use the OG-V series with larger clearances and PT100 compensation. A paint manufacturer in Vietnam bought a DN50 OG-V meter for solvent and resin batching at 800 cP. The meter runs 600 liters per hour and sends a 4-20 mA HART signal to the dosing system. That avoids manual weighing and speeds up batch time.

Last year a customer in Papua New Guinea asked us for a mechanical PD element for diesel backup generators. The site had 12 generators and no reliable 24 V DC supply. They selected DN25 OG meters with mechanical registers. The meters have run 18 months without repair. This is a typical use case for remote power and mining sites.

Installation Notes That Prevent Failure

PD meters do not need long straight runs. They do need clean fluid. Solid particles larger than 0.2 mm can jam the gears. Install a Y strainer or basket filter upstream. For high viscosity fluids, keep the meter heated or insulated. A drop in temperature raises viscosity sharply. This can overload the rotor and damage the bearing. So install a pressure relief valve if the line can be blocked downstream.

Here is the thing. Many failures come from air slugs. Air can spin the gears and overrange the counter. For truck loading and tank discharge, start with a full line. Install an air eliminator if the pump can draw air from the tank bottom. Flush the meter after use with a compatible solvent when the fluid can harden or gel.

FAQ: Displacement Meters and PD Elements

What is the typical accuracy of a PD meter for custody transfer?

Most Silver Instruments PD meters give plus or minus 0.5 percent of reading for liquids from 0.5 cP to 5000 cP. Repeatability is 0.03 percent. We provide a calibration certificate with each meter.

Do PD meters need straight pipe runs?

No. The measurement chamber isolates the rotating element from upstream disturbances. This is a major advantage in compact skids and on truck loading platforms.

Can a positive displacement meter run without power?

Yes. A mechanical register with a batch reset and non resettable total runs without power. Electronic options with 4-20 mA HART and pulse output need a loop supply or battery pack.

Which fluids are not suitable for oval gear PD meters?

Fluids with abrasive solids, non lubricating liquids such as water for some designs, and liquids with vapor slugs need special selection. Silver Instruments can supply PPS gears or PTFE seals for water and weak acids.

What information do you need for a quotation?

Send us the fluid name, viscosity in cP, pressure in bar, temperature in °C, pipe size in DN, flow range in liter per hour or kilogram per hour, and the output type. Our sales team will select a PD meter or a PD element for the application.

Send your application data to Silver Automation Instruments. Tel: +86-25-68650347. Whatsapp: +86-25-52155837. WeChat: +86 15365082610.

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