A two-stage pellet injector for Heliotron-E is constructed and tested. The aim is to increase pellet velocity for more flexible density profile control of the Heliotron-E plasma and also to conduct a pellet ablation study using a wider range of pellet velocity. The pellet velocity is limited to ∼1.4 km/s in the current six-pellet injector at Heliotron-E. The fundamental operation is simulated with the Quickgun code. The experimental results generally agree well (within 80 to 90%) with the code calculations. By using a newly developed high-pressure fast valve, a hydrogen pellet velocity of 3.2 km/s has been achieved without a supportive shell or sabot to protect the pellet, although more tests are needed to confirm whether pellets can reliably be accelerated to this high speed without fracturing. The dependence of the pellet velocity and breech pressure on the pump tube fill pressure is studied. The results show that the fill pressure is an important parameter. The effect of the clearance between the piston and the pump tube wall on the pellet velocity is also investigated. The wear and damage of the piston caused by the compressing propellant gas are investigated. It is shown that changes on the piston surface when hydrogen is used for fill gas are different from the case of helium.