Schneider Square D 9036/9037/9038 Electromechanical Liquid Level Controller

In the field of industrial liquid level control, Square D's 9036, 9037, and 9038 series electromagnetic liquid level switches have been widely used for decades for liquid level alarm and pump replacement control in water pumps, oil pumps, condensate tanks, sewage tanks, and hazardous areas due to their simplicity, reliability, and no need for external power supply. Although some models have gradually been replaced by electronic products, a large number of active devices are still in operation, and many OEM devices still specify the use of these classic products. Therefore, mastering its selection, installation, troubleshooting, and maintenance methods is still an essential skill for factory maintenance engineers and system integrators.

This article is based on original technical data and practical application experience to provide you with a complete maintenance guide for Square D liquid level controller. Whether you are dealing with an old 9036 float switch, selecting the 9037 series for a closed pressure tank, or repairing the 9038 mechanical alternators in a dual pump alternating control system, you can find the answer in this article.

Overview of product series and core principles of selection

1.1 Positioning of each of the three series

Class 9036- Open Tank Float Switch

Suitable for atmospheric environments such as open tanks, sewage tanks, cooling towers, etc. Divided into Type D (universal type) and Type G (heavy-duty type), as well as special Type FG (column sewage pump switch). The lever type action mechanism drives the micro switch through the floating ball to rise and fall with the liquid level. We can provide NEMA 1 (indoor universal), NEMA 4 (waterproof and dustproof), and NEMA 7/9 (explosion-proof) enclosures.

Class 9037- Sealed tank float switch

Used for sealing tanks such as pressure vessels, condensate tanks, and daily fuel tanks. Divided into Type E (flange installation) and Type H (2.5-inch threaded installation). The floating ball drives the switch through the connecting rod and adopts PTFE seal or nitrile rubber Quad ring seal, which can withstand a tank pressure of 50 psi. The temperature range is up to 220 ° F (ambient), and the medium temperature can reach up to 250 ° F (Viton) depending on the sealing material.

Class 9038- Mechanical alternators

Specially designed for alternating operation of dual pumps (or dual motors). When the liquid level rises, start one pump first; If the liquid level continues to rise to a high level, the second pump will be put into operation. When the liquid level drops, only the pump that started first stops, and the other continues to run until it reaches a low level. This pure mechanical alternating method avoids the complex wiring and fault risks of electrical alternators. We also offer three types of structures: open tank (Type A), threaded installation closed tank (Type C), and flange installation closed tank (Type D).

1.2 Selection Step 1: Clarify the Tank Type and Installation Method

Before selecting, please answer the following four questions:

Is the tank open or closed?

Open can → 9036 series (or 9038A for alternating)

Sealed tank → 9037 (single pump) or 9038C/D (alternating)

What is the installation interface?

Flange installation → 9037E, 9038D

2.5-inch thread → 9037H, 9038C

Ground or bracket installation → 9036 (optional 9049UMS1 universal installation board)

Environmental hazard level?

Ordinary indoor → NEMA 1

Damp, outdoor, requiring flushing → NEMA 4 (waterproof, dustproof)

Presence of flammable gases or dust → NEMA 7 (Class I, Div 1&2, Groups C, D) and NEMA 9 (Class II, Div 1&2, Groups E, F, G)

What is the required contact action method?

Close the contact when the liquid level rises (for drainage) → standard action (without suffix)

When the liquid level rises, disconnect the contact (for water replenishment) → Form R (reverse action)

Simultaneously provide normally open and normally closed → Form H (only partial 9036GG)

1.3 Electrical Rating Verification

The 9036, 9037, and 9038 series float switches can directly control low-power motors (up to 3 horsepower @ 240V single-phase, 5 horsepower @ 240V three-phase), or control high-power loads through contactors. Please ensure that the rated value of the switch is not lower than the motor nameplate data. For example, the 9036DG2 is rated for 2 horsepower at 115V single-phase and 5 horsepower at 230V three-phase. If used for control circuits (such as PLC inputs), the rated value of the control circuit is 600VA (AC).

For the 9038 mechanical interchanger, its internal N5 or N25 high water level alarm contact (single or double) is a quick action switch, with capacity as shown in Table 3 (e.g. disconnect 6A and connect 7.2A at 120V AC). Do not overload for use.

Correct selection of float and connecting rod - buoyancy and weight calculation

The reliability of the float switch depends on whether the buoyancy generated by the float is sufficient to overcome the resistance of the connecting rod, stop rings, and switch lever. The original factory provides two types of float ball accessory kits (Class 9049):