Modification of the unloader in reciprocating compressors

The main methods of flow regulation include those that act on the drive motor or drive mechanism, those that act on the gas piping, those that act on the gas valves, and those that utilize supplementary clearance for regulation. The following is a brief introduction to the common flow regulation methods. (1) Clearance volume adjustment method. By changing the effective clearance volume in the compressor cylinder, it is possible to adjust the amount of gas drawn into the compression chamber. Before fresh gas enters the compression chamber through the intake valve, the gas remaining in the clearance expands to the inlet pressure. When the clearance volume is large enough, the minimum exhaust volume of the compressor’s compression chamber can be reduced to zero. The disadvantage of the clearance volume adjustment method is high initial investment, and there are difficulties in space arrangement when it is located on the crankshaft side of the cylinder. (2) Unloading adjustment method. This regulation method involves installing a unloader on the intake valve of the cylinder in order to control the flow rate of the compressor; for single-acting double-acting cylinders, flow rate regulation at 0%, 50%, and 100% levels is possible ； For double-row single-acting cylinders, flow rate adjustment can be achieved at 0%, 25%, 50%, 75%, and 100%. Furthermore, friction of the air flow at the air valve generates heat, which leads to heat accumulation in the cylinder and raises its temperature. This method is generally only suitable for use during start-up and shutdown operations, and not for long-term operational adjustment. (3) Partially opening the suction valve adjustment method. This adjustment method involves installing a unloader with an actuator on the intake valve; during a portion of the exhaust stroke, the unloader keeps the intake valve open. The delayed closure of the intake valve allows some of the gas in the compression chamber to flow back into the intake pipeline; only after the intake valve closes (or is allowed to close) is the remaining gas in the cylinder compressed and expelled through the exhaust valve. Using this method, the adjustment range of the exhaust volume can reach nearly 60% (that is, from 100% full load to 40% full load). At maximum backflow, if the force of the airflow is not sufficient to overcome the unloading force, the air valve will remain open at all times, that is, in a fully unloaded state. (4) Bypass adjustment. Among all the regulation methods, the bypass method has the highest energy consumption. Its basic principle is to direct the excess compressed gas from the exhaust side of the compressor to the suction side through an intercooler and control valve, with the energy used to compress this excess gas being completely wasted. However, the bypass regulation is controlled by a control valve, enabling stepless automatic adjustment with a wide range and high reliability; it is particularly suitable for the precise automatic flow regulation requirements of petrochemical plants. (5) Active valve. With the advancement of electronic technology, gas valves can have their opening and closing controlled by mechanical devices. Some external mechanisms determine when the air valve opens and closes, with the pressure difference playing only a supplementary role in this process. It is a normal suction valve equipped with a unloading device, along with a specialized electro-hydraulic actuator. An electromagnetic valve used for electronic actuation allows a high hydraulic pressure to act on a small cylinder; the suction valve is opened by means of a unloader. When the hydraulic pressure in the small cylinder is released, the gas pressure in the cylinder acts on the valve element of the suction valve, causing it to close. To reduce the impact when the air valve opens, an appropriate opening moment can be calculated; moreover, a hydraulic damping system can reduce the impact when the air valve closes. The timing of the intake valve opening is not extremely important, but it should be slightly earlier than the moment when the pressure in the cylinder reaches the pressure in the pipeline. The closing time of the intake valve can start at any point during the compression process, allowing for stepless regulation of the compressor’s exhaust from 0% to 100%. (6) Adjusting the air volume can be achieved by replacing the drive motor with an inverter-driven motor or by adding a hydraulic coupler, etc.

1, 2, 3, 5 have not been tried； 4. In use, not economical ； 6. Is speed regulation achieved through variable frequency and hydraulic coupler control? Will the speed become too low after regulation, resulting in damage to the bearing shells (rated speed: 370 r/min)?

It won’t damage the tiles; it’s a feasible design and is commonly used!

It is necessary to clarify the design operating conditions, the requirements of actual operating conditions, the range of adjustment available, and the details of existing models – only then can a suitable solution be determined

2/4 and 5/6 are both useful to us, but we haven’t used 1/3 yet. It sounds like the third and fifth options are similar; are there any organizations in China that use it? Let me give some recommendations

We have a adjustment mechanism that allows us to tweak the production process according to the requirements, which also helps save electricity – achieving two goals at once. Feel free to call for inquiries at 13870209881:lol

You need to tell me about the design operating conditions and the actual operating conditions, as well as what your adjustment range is We can introduce the existing model options, so that it will be easier to determine a suitable plan.

The volume control system we produce allows for adjustment from 0% to 100% load, and it is capable of doing so

The variable flow control system we produce enables load adjustment from 0% to 100%, which helps maintain stability in the compressor’s operation. It also offers significant energy savings; for a 1MW compressor operating at an average load of 65%, this results in nearly 2 million units of electricity saved per year