STS Series Product Overview

STSSTS-T (Tank-Mounted)STS-TD (Tank + Dryer)

The STS series are single-stage, oil-injected screw air compressors designed for facilities requiring 5 to 30 horsepower of compressed air capacity. These units use a star-delta starter and a V-belt drive connecting the electric motor to the screw assembly. All STS compressors are controlled by the AirMASTER FORM controller (UL certified) and built to UL 508A and CSA C22.2 No. 14 electrical standards.

Model Variants

Model Designation	Description
STS-5 through STS-30	Standard cabinet-mounted compressor, 5–30 HP
STS-5T through STS-20T	Tank-mounted package — compressor integrated with a vertical air receiver
STS-5TD through STS-20TD	Tank-mounted package with integrated refrigerated air dryer

Key Specifications

Specification	Value
Compressor Type	Single-stage, oil-injected rotary screw
Starter Type	Star-delta
Drive	V-belt (motor to airend)
Cooling	Air-cooled (axial fan); water-cooled optional
Controller	AirMASTER FORM (UL certified)
Min. Ambient Temperature	+33.8°F (+1°C)
Max. Ambient Temperature	+104°F (+40°C)
Max. Operating Temperature	+230°F
Max. Altitude	3,280 ft above sea level
Max. Humidity	80%
Electrical Standards	UL 508A / CSA C22.2 No. 14

System Components

Oil System

The oil system consists of the screw assembly, separator tank, spin-on separator element (vertical/upward-flow), thermostatic valve, oil cooler, and spin-on oil filter element. A one-way check valve in the scavenge line returns separated oil from the separator element back to the screw assembly. The thermostatic valve bypasses the oil cooler until oil temperature reaches setpoint, then routes all oil through the cooler.

▲ Attention If ambient temperature exceeds +104°F (+40°C), oil temperature approaching the screw assembly should be at or above +122°F (+50°C). If the oil is too cold, condensation will form in the separator, causing corrosion and oil degradation that can seriously damage the screw assembly.

Cooling System

The STS uses an axial fan to draw cooling air through the cabinet. Hot discharge air must be ducted away from the compressor room and must not be allowed to re-enter the compressor intake. Duct air resistance must not exceed 50 Pa (5 mm H₂O).

Suction Control Valve — JF & HJF Series (NA Solenoid)

The STS series uses a JF or HJF series suction control valve with an NA (normally-open) solenoid valve and a venting valve. This is distinct from the STSH series (which uses the RB60E with an NC solenoid).

• Loading: When the NA solenoid energizes and closes, the venting valve opens. Pressurized air from the separator tank discharges through the suction control valve mouth, allowing the suction flap to open and air intake to begin.
• Unloading: When the NA solenoid de-energizes and opens, the venting valve closes. The suction control valve flap moves to the closed position and air intake stops.
• Auto-stop: If the compressor does not reach the lower pressure setpoint during the idle period, it stops. The separator tank depressurizes through the suction control valve discharge ports.

ℹ Note — High Pressure Models On STS models operating at 188 psi or above, the recommended control air operating pressure is 6 bar (87 psi), regulated by a pressure regulator at the suction control valve. Verify this setting during operation. Do not adjust.

V-Belt Drive

The motor drives the airend via V-belts. Belt tension must be checked every 2,000 hours. See the V-Belt Inspection & Replacement article for the full procedure. Always replace all belts in a set simultaneously and use the same brand — never mix belt brands or use belts of different specifications on multi-groove pulleys.

Tank-Mounted (STS-T) Lifting Note

▲ Attention — STS-T Models Only Tank-mounted compressors must be lifted using the forklift transport bar fixed between the air tank legs — not by the compressor cabinet. Center forklift forks on this bar and ensure forks pass completely through before lifting. Never lift by the compressor body or cabinet.

Optional Features

• Water-cooled heat exchanger: Optionally installed on the oil circuit line. Hot oil heats process water for industrial use. Water circuit must be active before first startup. Cooling water must meet quality and pressure specifications in the STS manual.
• Separator tank oil heater (125W): Optional resistance heater that warms oil in cold weather before startup, preventing screw assembly damage and reducing warmup-to-load time.
• Integrated air dryer (STS-TD models): Factory-installed refrigerated dryer. Monitor dryer function after every restart and at each commissioning visit.

Related Articles

• STS Maintenance Schedule
• V-Belt Inspection & Replacement
• First Start-Up & Commissioning Checklist
• Safety Precautions & Symbols

For technical support or commissioning, contact South-Tek Systems: [phone] or [e-mail]