If you look at the two images below, you will first notice there are more pieces to the valve assembly that comes on many of our home espresso machines (pictured on the left) compared to the compression style valve assembly (pictured on the right). The non-compression valve is the same valve used on many commercial machines. This type of valve is not only built to last but it's constructed so that it can be inexpensively repaired when necessary. The fact is that the non-compression valve can be rebuilt inexpensively while the compression style valve cannot, which must be replaced entirely. The non-compression type valve is held closed by the force of the spring, not by how tight you close it; you cannot put more pressure on the seat than the spring exerts.