Oil Free Gas Compressors for Liquid Transfer

Blackmer oil-free gas compressors deliver high efficiency in handling propane, butane, anhydrous ammonia and other liquefied gases. They are ideal for rail car unloading and vapor recovery applications. The single-stage, reciprocating compressors are designed to give maximum performance and reliability under the most severe service conditions. All pressure parts are of ductile iron construction for greater resistance to both thermal and mechanical shock. They are designed for ease of maintenance, with all components readily accessible.

Models are available with capacities from 7 to 125 cfm (11.9 to 212 m³/h) with working pressure up to 350 psia (24.13 Bar).

Gas Compressors for Liquid Transfer

Many liquid transfer applications can be handled more efficiently with a gas compressor than a liquid pump. They include unloading of transports and pressure vessels where system piping restricts flow and may cause a pump to cavitate; unloading of LP gas from rail cars, and other installations that require an initial lift to the liquid.

How Liquid Transfer is Accomplished

When transferring liquid, a compressor creates a slight pressure differential between the vessel being unloaded and the receiving tank. The suction stroke of the compressor piston draws in vapor and decreases the receiving tank pressure. The discharge stroke moves a measured volume of vapor at a higher pressure into the supply tank where it displaces an equal volume of liquid through a separate line into the receiving tank. Generally, the liquid flow rate will be 5 to 6 U.S. gpm for each cubic foot (ft3) of piston displacement (670 - 775 liters per cubic meter [m3]).

Propane Vapor Recovery

The chart and graph illustrate typical volumes of liquid that may be recovered at various pressures and operating times, based on a 33,000 U.S. water gallon capacity (124,915 liters) tank car – using a Blackmer LB361 gas compressor with 36 CFM (60.3 m3/h piston displacement).

For example, when the liquid transfer phase of unloading is completed, the vapor pressure reads 150 psig (10.34 Bar gauge). At this condition, there would be approximately 1,315 U.S. gallons (4,978 liters) of LP gas in vapor form remaining in the tank car. Of this amount, 845 U.S. gallons (3,199 liters) can be economically recovered in less than three hours.

Technical Specifications

High efficiency valves move more gas volume

The heart of any compressor is its valve assembly and Blackmer valves are specifically designed for non-lubricated gas applications. With precisely engineered clearances, spring tension, and a special finish, these valves seat more positively so more gas is moved with each piston stroke. Blackmer valves offer greater strength, quiet operation, and long life.

O-Ring seals - head and cylinder

The head and cylinder are sealed with O-rings to ensure positive sealing under all operating conditions.

Pressure assisted piston rings for positive seating

Constructed of self-lubricating Teflon®, Blackmer’s special ring design provides maximum sealing efficiency with minimal friction wear. The result: peak performance and extended compressor service life.

Heavy-duty crankshaft

The ductile iron crankshaft is precision ground with integral counterweights for smooth, quiet operation. Rifle drilling ensures positive oil distribution to the wrist pin and connecting rod bearings.

Ductile iron pistons

Heavy-duty ductile iron pistons are connected with a single positive locking nut which eliminates potential problems associated with more complex designs.

Self-adjusting piston rod seals

Crankcase oil contamination and cylinder blow-by is prevented with loaded glass-filled Teflon® seals which maintain a constant sealing pressure around the piston rods.

Ductile iron construction

All pressure parts are of ductile iron for greater resistance to both thermal and mechanical shock

Wear-resistant crosshead assemblies

Designed for maximum lubrication and wear resistance.