With the COMAR product line, FRAKTA Vertriebs GmbH offers an interesting series of control valves in short-stroke design. Although the valves have been available on the market for several years, they are still too little known, at least in Germany. Therefore we will present them in more detail in the following.
COMAR Control Valves of FRAKTA Vertriebs GmbH
Structure of short-stroke valves
Most short-stroke valves on the market have a built-in spring that pushes the valve tappet upwards. This means that the actuator only has to exert force in the extending direction and push the valve stem downwards. In the opposite direction, it acts as a resistance against the spring force of the valve tappet so that it only moves to the position specified by the control signal. The actuator therefore does not have to pull, as the valve tappet automatically follows the retracting movement of the actuator by the spring. This also eliminates the need for a mechanical coupling between the actuator and valve tappet, which certainly leads to savings in the manufacturing effort required for the valve and actuator.
Disadvantages of this design
But this design also has disadvantages. On the one hand, the valve actuator requires a relatively large amount of force, as it must overcome not only the resistance of the medium flowing through the valve but also that of the built-in spring in one direction of movement. So this requires a more powerful drive. On the other hand, the actuator would "not notice" if the valve tappet were blocked in the retracting direction of the actuator. There is no mechanical connection between the valve plunger and the actuator plunger. The electronics of modern drives register blockages in the travel and send a corresponding signal to the higher-level control system. In that case, she can't. The actuator would move to the specified position without the valve following. The error would only occur later if the desired parameter value (e.g. the desired water temperature) is not set in the system.
The FRAKTA variant
The COMAR control valves from FRAKTA therefore do without the spring and implement a coupling mechanism on the actuator together with a counterpart on the valve. However, the actuator can be mounted on the valve just as quickly as on the short-stroke valves with spring. Here, too, the actuator is only screwed onto the valve. The coupling takes place automatically when voltage is applied to the drive. Manual coupling and adjustments are not necessary. And smaller and less expensive valve actuators can be used.
The COMAR series comprises 2- and 3-way valves with screw connection (male thread) with threaded or weld-on fittings and with flange connection. The latter is a unique selling point in this valve class. Fittings are always included in the scope of delivery. The inner housing geometry is optimally designed for the respective valve type (2- or 3-way). In other words, the 2-way valves do not have a 3rd port which is closed with a washer together with a union nut. Thus, the 2-way housings are fluidically optimized and do not represent a compromise.
The nominal diameters range from DN15 to DN40 with the usual Kvs values. However, the DN15 valves are already available with very small Kvs values (globe valve from 0.16 m3/h, 3-way valve from 0.25 m3/h) for which small valves with a nominal diameter of DN10 are otherwise required. This allows the COMAR series to cover a wide range of applications, especially since the nominal pressure is PN16. The temperature range for the medium flowing through is from 2 to 130 °C. The control ratio is 50:1 and the very low leakage rate is below 0.0001% of the respective Kvs value. This ensures a high control quality with low energy losses.
The housing is made of grey cast iron, which is painted abrasion-resistant for corrosion protection. The interior fittings are completely made of stainless steel. It is therefore of much higher quality and more durable than control valves of other manufacturers. This is because the inner fittings of short-stroke valves are often made of brass. The stuffing box is sealed with an EPDM O-ring.
Of course, the COMAR series also includes corresponding valve actuators with 250 or 500N actuating force. The 230V variants operate with 2- and 3-point control. The 24V drives can be controlled 2-point, 3-point and continuous (0...10 V DC). Possibly necessary auxiliary switches can be plugged on as an additional module.
The assembly of the drives is very simple. They are attached to the valve and hand-tightened with a knurled nut. The valve and actuator tappets are coupled automatically as soon as voltage is applied to the actuator. Adjustment work is completely eliminated.
The list prices start at 86.00 EUR (DN15) for the 2-way valves with screw connection and end at 125.00 EUR (DN40). For the 3-way valves, the price range is from 90.00 to 137.00 EUR. As mentioned, the fittings are included. For the valves with welded connections, the prices are only a few euros higher in each case. Somewhat larger are the price differences to the flanged versions (globe valve 112.00 to 190.00 EUR, 3-way valve 146.00 to 228.00 EUR). However, compared to the flange valves with similar technical data available on the market, even this is still very favorable. Just compare with the valves you usually use and make up your own mind.
With the COMAR series, FRAKTA offers control valves that are technically more than able to keep up with comparable products from other manufacturers. And the COMAR valves offer tangible advantages in terms of price. Detailed information and the download of the data sheets can be found here on the website: