HMI Excess Flow Check Valves are normally open safety valves for installation in lines flowing into and out of pressure tanks. Their main function is to stop the full flow of the tanks liquid contents automatically should a flow line rupture and reset automatically when repairs are made. Therefore, they should be installed in the tank fitting or as near as possible to the tank.

HMI Excess Flow Check Valves are reliable, simple, totally mechanical and very effective. When a line breaks the increased velocity of flow creates a pressure drop across the valve which over comes the preset maximum flow setting of the valve and the valve closes. After the excess flow check valve is triggered it will remain closed until the flow line is repaired and the pressure is balanced automatically across the valve.

HMI Excess Flow Check Valves can be used in other piping systems to limit flows to a predetermined maximum flow. The excess flow check valve will allow flow in either direction but will only trigger in the specified flow direction.

Each HMI Excess Flow Check Valve is designed for a particular flow application and maximum flow rate. It will flow any rate less than this rate but will close when this rate is exceeded. Slight weeping will occur when closed, this is normal, it allows the valve to reset automatically to the normally open position after repairs are made.

Installation & Testing:

Excess flow check valves should be installed in lines flowing into and out of pressure tanks. Installation should be as near as possible to the tank. After installation, excess flow check valves should be periodically inspected to ensure they function as intended.

A quick way to demonstrate whether the excess flow valve is working properly is to increase the flow rate over the rated capacity of the valve. The valve, if working properly, will close due to the increased flow velocity. Of course, make sure this testing method is acceptable for your situation and that it does not pose a hazard or damage equipment.

Cautions & Warnings:

Helmco recommends periodic inspection of any excess flow check valve. Failure to do so could result in valve failure when it is needed which could cause damage to equipment, i.e. pumps, etc. or in some cases cause personal injury or death. HMI Excess Flow Check Valves are inspected and tested before shipment to ensure they flow the customer specified maximum flow rate and close when the maximum flow rate is exceeded. It is the customers responsibility to install the excess flow check valve properly and in accordance with certain regulatory agencies, if any, and to periodically inspect/test in accordance with the customers preventive maintenance schedule and keep a record of these inspections. HMI recommends inspection and testing all excess flow check valves at intervals not exceeding one year.

The single most important warning for excess flow valves is:

This can only be accomplished thru routine maintenance and testing. This not only checks the condition of the excess flow valve but will also alert the operator if the proper valve has been selected and if it has been installed properly.

Reasons excess flow valves fail:

1. Upstream pressure too low to produce an excess flow.

2. Too many restrictions downstream in the piping system ( example: reduction of pipe size, length of downstream pipe too long, too many fittings, a partially closed valve downstream.

3. A flow line downstream has ruptured but the break is not large enough to cause an excess flow (example: a split or tear in the flow line).

4. Foreign material lodges in the valve preventing it from closing.

5. Tampering with the excess flow valve by attempting to get more flow than the valve was designed for.

6. Prolonged hammering of the excess flow valve, which damages the valve.

Do not oversize an excess flow check valve. To do so will cause the valve to never be subjected to an excess flow because the valve would be set to trigger at a flow rate higher than you are capable of flowing. Example: You are capable of pumping 300 gpm maximum thru a line without an excess flow check valve. You install an excess flow check valve set to trigger at 500 gpm. The valve will never close because it will never be subject to a flow over 500 gpm.

Do not reduce downstream piping smaller than the rated size of the excess flow valve. Do not add other restrictions downstream such as too many valves, fittings, flow meters or excessive piping. Testing the excess flow valve after installation will reveal if it is installed properly and is recommended by HMI.

HMI offers an in-house re-manufacturing service on HMI Excess Flow Check Valves should the customers maintenance personnel determine the excess flow valve is in need of repair or calibrating. Simply return the valve prepaid to HMI and we will evaluate the valve and inform you the cost to repair. In most cases, repairs and calibrating are less than half the cost of a new excess flow check valve.

All HMI Series Excess Flow Check Valves are near chatterless due to our improved design which should greatly extend the service life of the excess flow valve. However, any excess flow check valve of this type can be made to hammer. Some operators have the misconception that the excess flow check valve is flowing it's maximum capacity when it is hammering. In fact, the flow is greatly reduced at this point and prolonged hammering will damage the valve which can lead to valve failure or damage to equipment and possible injury or death.

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